I can only get it work if all the values are nan and you are using mean. Show 3 older comments. I have data in excel that is 17 columns by 4800 rows. This MATLAB function returns the sum of the elements of X, computed after removing all NaN values. Show 3 older comments. There. There is a function to find the number of nonzero matrix elements nnz. If DIM is not specified, it defaults to the first non-singleton dimension of A. e. R2022a Update 2 Installation Files can not be used to install a toolbox to R2022a Update. m = moment (X,order,vecdim) returns the central moment over the dimensions specified in the vector vecdim. If X is a multidimensional array, then nanmean operates along the first nonsingleton dimension of X. % the average to another ThingSpeak channel. However, the piece of code that I use to implement it takes up atleast 80% of the runtime (approximately 4s out of the total 5s). use nansum: y=nansum(x); %x is the array name 0 Comments. symsum (f,k, [a b]) or symsum (f,k, [a; b. You can mask your array using the numpy. Field. Teams. Birdman on 13 Feb 2018. This arrays contains also NaNs, but I need to computer a proper mean value of them later. {"payload":{"allShortcutsEnabled":false,"fileTree":{"":{"items":[{"name":"calendar","path":"calendar","contentType":"directory"},{"name":"cm_and_cb_utilities","path. A new array holding the result is returned unless out is specified, in which it is returned. Y=mean (X,dim,'omitnan') 4 Comments. [i,j] = find (X) returns the row and column indices of the nonzero entries in the matrix X. in the date column, time is not given but it is. You do not need to change the input arguments. numpy. y = nansum(X,vecdim) returns the sum over the dimensions specified in the vector vecdim. MATLAB 함수 sum 을 대신 사용하십시오. MATLAB has a few functions to deal with this situation: NANMEAN, NANMEDIAN, NANSTD, NANMIN, NANMAX, NANSUM. 8, np. % Input Arguments:That's a difficult problem to vectorize. g. Becasue that also would not work. y = nansum(X,vecdim) returns the sum over the dimensions specified in the vector vecdim. E. Find more on Creating and Concatenating Matrices in Help Center and File. height=height (~isnan (height)) data=data (~isnan (data)) 4 Comments. . Edited: Stephen23 on 5 Jan 2016. Show 2 older comments Hide 2 older comments. R2022a Update 2 Installation Files can not be used to install a toolbox to R2022a Update 3 MATLAB. Each element of the output array is the. you cannot install a toolbox for MATLAB R2022b into MATLAB R2023a. Sorted by: 3. Return the cumulative product of elements along a given axis. In. g. y = nansum(X,vecdim) returns the sum over the dimensions specified in the vector vecdim. Undaunted, I wrote my own version of nancumsum and promptly shared it on the File Exchange. I want to calculate the monthly mean for each year and then calculate average for 10 years. SO2gm3)); outij =. function m = nanmean (x,dim) %NANMEAN Mean value, ignoring NaNs. To update your code, change instances of the function name nanmin to min. nan, a) # Set all data larger than 0. nansum(A) % Requires Statistics toolbox Code tested using MATLAB R2018b. g. For matrix input, M is a row vector containing the mean value of. Don’t use min for element-wise comparison of 2 arrays; when a. The function computes the sums after removing NaN values. . There are no plans to remove nanmin. For example, if X is a 2-by-3-by-4 array, then moment (X,1, [1 2]) returns a 1-by-1-by-4 array. Example. % If your channel is private, then enter the read API Key between the '' below: % Get Output Liquid Quantity data for the last 30. Syntax. How numpy handles numerical exceptions #. 8,175 1 1 gold badge 39 39 silver badges 31 31 bronze badges. % in Natick, Massachusetts. nanmean giving nansum output. You can always use nansum from the stats toolbox. ExamplesDesigned for the way you think and the work you do. Standard deviation ignoring NaNs. By default the input is flattened. x = linspace (0,10); y = sin (x); plot (x,y); Set the x -axis limits mode to manual so that the limits do not change. Look with this new sample data where there is a row where both are nan. Syntax. symsum (f,k, [a b]) or symsum (f,k, [a; b. For example, we might want calculate the mean of all values that are not NaN. Raw Blame. nansum calls the _replace_nan function. 1. Show -1 older comments Hide -1 older comments. you cannot install a toolbox for MATLAB R2022b into MATLAB R2023a. 1. For example, if X is a matrix, then nanmean (X, [1 2]) is the mean of all non- NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. nansum 은 권장되지 않습니다. Depending on your signal, using a linear interpolation can make sense. , you can use the 'nan' variant of those functions: nansum, nanmean, nanstd, nanmax, nanmedian. y is the sum of the non-NaN elements in X. This arrays contains also NaNs, but I need to computer a proper mean value of them later. Option 1: toolbox free solution using sum and isnan from base MATLAB. S = sum ( ___,outtype) returns the sum with the. ¶. If f is a constant, then the default variable is x. : Toolboxes must match the release of MATLAB they are installed into, e. nanmean arithmetic mean, ignoring NaNs;. Show 1 older comment Hide 1 older comment. The function computes the sums after removing NaN values. Hello, I am reciving a message from MATLAB saying that 'nansum' use is not reccomended and to use 'sum' instead, with the appropriate code changes. random. the first column is dates the second column is temperature- here I want to find daily max and min the third column is rainfall- here daily sum I don't need 4th and 5th column but for this time make an average. NaN is a special floating-point value which cannot be converted to any other type. When I type >>help nansum in the command window, matlab returns "nansum not found. The fplot documentation describes that its function input (usually the first input) ". This syntax is equivalent to imdilate (I,strel(nhood)). you cannot install a toolbox for MATLAB R2022b into MATLAB R2023a. These variants basically discard ignore nan values when performing calculations. NaN values are propagated, that is if at least one item is NaN, the corresponding max value will be NaN as well. nanstd. If f is a constant, then the default variable is x. It is also used for representing missing values in a dataset. It also works with multidimensional indexing. At least you need to use something sufficiently recent that sum will include that option. For matrices, nanstd(X) is a row vector containing the standard deviations of the non-NaN elements in each column. nansum 을 제거할 계획은 없습니다. The output for the last row of y returns NaN (a copy of the command window is shown below). Edited: Stephen23 on 5 Jan 2016. % non-NaN elements in each column. Then do the grouped calculation, and convert the grouping variable's unique values back to datetime: Theme. If A is a multidimensional array, then sum (A) operates along. The method, which was proposed in a recent paper by Sievers et al. the help command (image below) is also referencing nansum's functionality. hist3 (X,'Nbins',nbins) specifies the number of bins in each dimension of the histogram. The laws differ from country to country and state to state. {"payload":{"allShortcutsEnabled":false,"fileTree":{"":{"items":[{"name":"calendar","path":"calendar","contentType":"directory"},{"name":"cm_and_cb_utilities","path. numpy. By refactoring, you save yourself some needless comparisons, assignments,. If you want to include NaN values, then specify the 'includenan' option for the nanflag input argument. I find the products and only sum on the products that produce a real number (eg 1*nan=nan therefore. For real values of X, atand (X) returns values in the interval [-90, 90]. But removing nanmean, nansum, nanstd, etc from the basic Matlab was a serious mistake. sum. Learn more about matlab array sum find MATLAB. Learn more about matlab function MATLAB function 'nanmean' is behaving like nansum and I don't know why. the help command (image below) is also referencing nansum's functionality. MATLAB Language Fundamentals Matrices and Arrays Creating and Concatenating Matrices. shape[0] is 2, minimum(a[0], a[1]) is faster than min(a, axis=0). and that's interesting to see why nanmean is not preferred. The data is collected once every day. nansum. nanstd () function compute the standard deviation along the specified axis, while ignoring NaNs. yang-En Hsiao on 26 Mar 2019. NMODE: specifies how NaNs should. If you are you used to 255 color values from HTML for example, you can divide by 255 to get a value between 0 and 1. To test if an element is NaN, use the function isnan . axis : [ {int, tuple of int, None}, optional] Axis along which the. I have data of water level (both maximum and minimum in a scale of the meter) on a daily basis for a certain number of years. The function computes the sums after removing NaN values. Các ký tự && và || là các toán tử logic short. [Z_downsamp,t_downsamp] = downsample_ts (. This function declares an input argument that must be a vector of doubles containing no NaN elements. so I thought you use nanmean and nansum to ignore nans with grpstats, but it seems that it always ignores them. Aman Kumar on 29 May 2020. defining the loop with for k=1:size (CP), which may not be giving you the range that. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. Hello! I would like your help on my issue. % If your channel is private, then enter the read API Key between the '' below: % station channel. The cumulative sum does not change when NaNs are encountered and leading NaNs are replaced by zeros. Show 2 older comments Hide 2 older comments. the help command (image below) is also referencing nansum's functionality. I want that the result matrix contains only a NaN value if A has NaN or if A has a value but B, C and D do all have a NaN value. Y = nansum (x [,DIM]) DIM dimension 1 sum of columns 2 sum of rows default or []: first DIMENSION with more than 1 element Y resulting sum see also: SUM, SUMSKIPNAN, NANSUM. For simplicity, lets pretend that only the second fraction of the equation is there. 3 Comments. for i=1:length(shapefile)It is used to represent entries that are undefined. Field. This MATLAB function returns the sum of the elements of X, computed after removing all NaN values. If A is a vector, then prod (A) returns the product of the elements. I have 12 matrices, each of size 30x53x351. Find the treasures in MATLAB Central and discover how the community can. Syntax. Below are additional functions (© Kara. If installing the toolboxes offline, the installation files must match the update version of MATLAB, e. 2 Answers Sorted by: 3 You can achieve this without using any specific function call just by setting the NaNs to 0s and then performing the sum: A (A~=A)=0 B. Description. I have 6 2D matrices. The hist3 function displays the bins as 3-D rectangular bars, and the height of each bar indicates the number of elements in the bin. abs) Find sum of elements of updated matrix (using np. L1 = 75; L2 = 130; L3 = 125; L4 = 60; L5 = 130;m = moment (X,order,dim) takes the central moment along the operating dimension dim of X. Just keep track of where all elements are NaN, and replace their sum with NaN after using nansum. e. y = nansum (X) returns the sum of a financial time series object X , treating NaN s as missing values. Bish Erbas on 27 Sep 2018. y = nansum (X) returns the sum of a financial time series object X , treating NaN s as missing values. Copy. Syntax : numpy. First, plot a line. The function computes the means after removing NaN values. Also several functions from Matlab have no. Contrary to the matlab code, this also works for values different from 1. A common fix for rthis is the modified median filter. Unbiased estimates are provided. nansum to sum up the values ignoring NaNs after element-wise multiplication -. g. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. . y = nansum(X) returns the sum of a financial time series object X, treating NaNs as missing values. example. Finall. Jan el 4 de Nov. Accepted Answer. To test if an element is NaN, use the function isnan . If DIM is not specified, it defaults to the first non-singleton dimension of A. I need to devide vector by vector, ignoring elements with zero in the denominator. Use hold on to add a second plot to the axes. The default multiply puts nan down the whole column of the result where there was even a single nan in the data. Also, using nansum() is not recommended as you can see from its documentation page. mat. nansum, nanmean, etc. Select Lowess Fit Interactively. 4. The modules implement the regularized EM algorithm described in. m(release 2018b) function returns zero when all entries are NaNs. There is a nansum function in Statistics and Machine Learning Toolbox that accepts regular numeric (including double precision) data. You can set the regression. So far I have done this for column B: Theme. I have a 736x1 vector, called 'ARRAY4' which I. For vectors, nanmean(x) is the mean of the non-NaN elements of x. jl and DataArrays. Before evaluation, you can get rid of nans as follows: Theme. Learn more about nansum, function, monthly_sum MATLAB I use the function below to perform the monthly precipitation accumulator, however, when there are days without NaN measurements in a given month, the result for that month is zero. See also: mean, nanmin, nanmax, nansum, nanmedian. hist3 (X) creates a bivariate histogram plot of X (:,1) and X (:,2) using 10-by-10 equally spaced bins. Searching the MATLAB documentation, I quickly found my way to nansum in the Statistics and Machine Learning Toolbox. The size of this dimension becomes 1 while the sizes of all other. I can suggest a way to do it using CELLFUN, but I can't guarantee that it will be faster for your problem (you would have to time it yourself on the specific data sets you are using). Learn more about nan, nansum, multidimentional, array MATLAB Hello, I need to sum some multidimentional arrays after SPMD processing. Made for data-oriented projects in general; Open-source; Handles big data (very large datasets) Large number of ready-made packages; Built-in ways to professionally visualize data{"payload":{"allShortcutsEnabled":false,"fileTree":{"":{"items":[{"name":". MATLAB ® apps are interactive applications written to perform technical computing tasks. % values. nansum for financial time series. The Matlab statistics toolbox has the functions nanmax, nanmean, nanmedian, nanmin, nanstd and nansum that do precisely that. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. 每个单元包含一个200x150矩阵。. USAGE: B = nancumprod (A, DIM, NMODE) ARGUMENTS: A: Input matrix. Theme. I want to run fast Matlab algorithms over Matrices by ignoring zero-elements. The function computes the sums after removing NaN values. The function computes the sums after removing NaN values. You need to use your organization email address in your MathWorks Account to link to the license. For matrices, nansum (X) is a row vector containing the sum of the non- NaN elements in each column of X. nansum(arr, axis=None, dtype=None, out=None, keepdims=’no value’) 参数 : arr :[array_like] 包含数字的数组，其总和是需要的。如果arr不是一个数组，将尝试进行转换。 axis :计算总和的一个或多个坐标轴。y = nansum(X,vecdim) returns the sum over the dimensions specified in the vector vecdim. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. nansum()函数用于计算一个给定轴上的数组元素的总和，将非数字（NaNs）视为零。 语法 : numpy. g. nancumsum: Cumulative sum of a matrix, with user-specified treatment of NaNs. Steven Lord el 4 de Nov. The different behaviors are: ‘ignore’ : Take no action when the exception occurs. (Note, NANSUM from Matlab does not support the DIM-argument, and NANSUM(NaN) gives NaN instead of 0); 4) Defining the estimation mode (biased or unbiased) This feature is removed. The problem remain the same. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. the help command (image below) is also referencing nansum's functionality. Help, here is my code. The app uses locally weighted linear regression to smooth the data. The function computes the sums after removing NaN values. The 17 columns represent different muscles, and the rows represent times they are "activated. Learn more about matrix manipulationHello, I am reciving a message from MATLAB saying that 'nansum' use is not reccomended and to use 'sum' instead, with the appropriate code changes. The question have sort of already been answered before here, but I can seem to get the suggestion to work:. In MATLAB = is used only to assign a value. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. Los navegadores web no admiten comandos de MATLAB. where(a > 0. ) didn't install correctly, were they not included in R2011a, or do they exist under a new name? Thanks!downsample_ts. F = symsum (f,k,a,b) returns the symbolic definite sum of the series f with respect to the summation index k from the lower bound a to the upper bound b. along the dimension of A specified by scalar DIM. Matlab 使用NAN添加2x2矩阵,matlab,sum,nan,Matlab,Sum,Nan,与其说是寻找编程建议，不如说是一个普通的MATLAB问题——如果我有： y = cellfun(@(x)sum(x(:)), Z, 'un', 0); 如果每个单元格矩阵中都有NaN和实数的组合，当我对每个单元格中这些矩阵的所有元素求和时，我是否总是得到total=NaN，因为其中有NaN，或者它们将被. Hi Sara, here is an available function for detrending with NaNs. Improve this answer. Show 2 older comments Hide 2 older comments. Description. Edit: Another way of achieving this as @rayryeng suggested in the first comment is to use isnan: A (isnan (A))=0 B (isnan (B))=0 C=A+B. 5) The DIMENSION argument is implemented in most routines. Note that nansum(A,dim) is the same as sum(A,dim,'omitnan'). Learn more about nansum, function, monthly_sum MATLAB I use the function below to perform the monthly precipitation accumulator, however, when there are days without NaN measurements in a given month, the result for that month is zero. Specifically, the source code for np. The sum () function returns NaN if there are NaNs in your array, if that behavior is what you want. % in Natick, Massachusetts. Learn more about nansum, function, monthly_sum MATLAB I use the function below to perform the monthly precipitation accumulator, however, when there are days without NaN measurements in a given month, the result for that month is zero. If A is a matrix, then sum (A) returns a row vector containing the sum of each column. If X is a matrix, then nanmean(X) is a row vector of column means, computed after removing NaN values. 関数 nansum は推奨されません。代わりに、MATLAB 関数 sum を使用してください。nansum が削除される予定はありません。 コードを更新するには、関数名 nansum のインスタンスを sum に変更します。次に、入力引数 nanflag に 'omitnan' オプションを指定します。 Numeric integration in Matlab. Toggle navigation. Toolboxes must match the release of MATLAB they are installed into, e. In my nested loop format I run through every column of B for each row of A. For vectors, nansum(x) is the sum of the non-NaN elements of x. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. +100. I am trying to calculate a cosine similarity using Python in order to find similar users basing on ratings they have given to movies. for lambda=280:2500 numerator (lambda) = trapz (Einc (lambda:lambda+1)*St (lambda)); denominator (lambda) = trapz (Eref (lambda:lambda+1)*St (lambda)); end. Melden Sie sich bei Ihrem MathWorks Konto an;nansum是Matlab概率统计函数的第34集视频，该合集共计59集，视频收藏或关注UP主，及时了解更多相关视频内容。 公开发布笔记 首页{"payload":{"allShortcutsEnabled":false,"fileTree":{"matlab":{"items":[{"name":"QU_KEMAR_AKGK601_hcomp. For multidimensional arrays X, nanmedian operates along the first. To test if an element is NaN, use the function isnan. , sort function will always arrange NaNs at the top end. Is it possible that these functions (i. wav","contentType. nansum()函数用于计算一个给定轴上的数组元素的总和，将非数字（NaNs）视为零。. For matrices, nansum(X) is a row vector containing the sum of the non-NaN elements in each column of X. for lambda=280:2500 numerator (lambda) = trapz (Einc (lambda:lambda+1)*St (lambda)); denominator (lambda) = trapz (Eref. e. Don’t use max for element-wise comparison of 2 arrays; when a. I have an excel file (see attached) that contains daily pollution data from 2006-2016. m = magic(3); m([1 6 8]) = [NaN. Reviews (22) Discussions (7) The collection of functions in the NaN Suite enhances the functionality of the original 'nan'-functions in the Statistics Toolbox for N-D matrices. Steven Lord on 4 Nov 2016. >> d = datetime (2015,1,1) + caldays (randi (2,5,1)); nanmin is not recommended. example. numpy. Learn more about nansum, nanmean Hi Mathworks I have had a lot of luck with previous questions, so I will try once more. Steven Lord on 4 Nov 2016. Return the sum of array. cumprod #. Computes the cumulative product of matrix A along dimension DIM, allowing the user to replace NaNs with ones, or to maintain NaNs as placeholders. Description. 167 0. Ralph Andrews on 13 Feb 2023. % the average to another ThingSpeak channel. Toolboxes must match the release of MATLAB they are installed into, e. function cx_value = cx( alpha, el ) A = [ -0. The function computes the sums after removing NaN values. Sign in to answer this question. Learn more about nanmean, error, despike Hi guys, in Matlab the output of functions ksdensity and mvksdensity do not sum to one. '); return else return end. Viewed 10k times. We have set it to float 64 bits to avoid overflow. nansum (a, axis=None, dtype=None, out=None, keepdims=<no value>, initial=<no value>, where=<no value>) [source] # Return the sum of array elements over a given axis treating Not a Numbers (NaNs) as zero. It is important to learn that in floating point number convention NaN is not equal to anything, not even itself. You can use nansum. numpy. Hi everyone, I don't have any toolbox, but I thought these functions are built-in for 2013b, no? Thanks, Karen. To ignore NaN values (MATLAB behavior), please use nanmax. Answers (1) Naomi Krauzig. Return the sum of array elements over a given axis treating Not a Numbers (NaNs) as zero. In NumPy versions <= 1. numpy. The function computes the sums after removing NaN values. m. Copy. nansum. nanmean (a, axis=None, dtype=None, out=None, keepdims=<no value>, *, where=<no value>) [source] # Compute the arithmetic mean along the specified axis, ignoring NaNs. As it can be expected there are a lot of NaN values. Berry, and Peter Huybers. SO2gm3)); outij = sortrows ( [ii jj]); length (outij) One work-around would be to temporarily convert the datetime to a numeric representation (for example, the number of seconds since some reference time). See syntax, description, input and output arguments, and examples of nansum in MATLAB. The convolution operator is often seen in signal processing, where it models the effect of a linear time-invariant system on a signal [1]. It is a good idea to use parentheses to explicitly specify the intended precedence of statements containing combinations of & and |. I guess the reason for the NaN-in NaN-out behaviour of many functions in Matlab (such as sum, std, mean, median, corrcoef, detrend) is thatBy default, nanstd normalizes y by n – 1, where n is the number of remaining observations after removing observations with NaN values. In Numpy versions <= 1. Since the above computation works fine for me using R2016a, you are using an older release. However, I run into problems with 0 values. For matrices, nansum (X) is a row vector containing the sum of the non- NaN elements in each column of X. For simplicity, lets pretend that only the second fraction of the equation is there. #. To add a bit of context to the question of nansum on empty results, we currently differ from MATLAB and R in this respect, they return zero no matter what. do something with x(i,j) end end end But how can I make the matrix operation on the whole matrix x?y = nanmedian(X) is the median of X, computed after removing NaN values. Task Removed Functionality Use This Functionality; Merge multiple time series objects: merge(fts1,fts2) [TT1;TT2] (requires variable name to be the same) unique(TT) Concatenate financial time series objects horizontallyor var or mean) using only the non-NaN values. If A is a multidimensional array, then sum (A) operates along. nancumprod: Cumulative product of a matrix, with user-specified treatment of NaNs. nansum# numpy. I know this sounds like an easy question. However, I have data that needs to be operated. NaN values are propagated, that is if at least one item is NaN, the corresponding min value will be NaN as well. If dtype is not specified, it defaults to the dtype. Learn more about matlab array sum find MATLAB. y = nanmean(X,vecdim) returns the mean over the dimensions specified in the vector vecdim. Trong MATLAB, các hàm được định nghĩa trong các file riêng biệt. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. Learn more about neural networks, feedforward network I am created one small neural network and I am trying to program that network. cumprod. numpy. Up until Julia 0. k = nansum(r) Or pick the non nan's and sum them. vector3d; abs; accumarrayHello! I would like your help on my issue. As explained on github, accumarray now supports nan-prefixed functions (e. If my answer helped you can accept it so that others will know that this question has been solved. Often you wont see any affect (for instance using max or sum in this way simply returns the inputs [1]), but nansum replaces NaN with zero, so that's all that happens. J = imdilate (I,nhood) dilates the image I, where nhood is a matrix of 0 s and 1 s that specifies the structuring element neighborhood. If you just want to find the length of the column (not including nan entries), here's an example:nansum() is an older routine that is part of the Statistics Toolbox. At least you need to use something sufficiently recent that sum will include that option. nancumsum. For example, if X is a matrix, then nansum(X,[1 2]) is the sum of all non-NaN elements of X because every element of a matrix is contained in the array slice defined by dimensions 1 and 2. Learn more about nanmean, error, despikeHi guys, in Matlab the output of functions ksdensity and mvksdensity do not sum to one. NANMAX (A,DIM) calculates the maximum of A along the dimension DIM of the N-D array X. I have added an explanation and numpy implementation. The rows are the time and the columns are the space. It's just named "the sum function called with the 'omitnan' flag. shape[0] is 2, maximum(a[0], a[1]) is faster than max(a, axis=0).