MATLAB: How to have the “Matrix dimensions must agree” error message show the sizes of the matrices involved

MATLAB

When developing code, it would be useful if MATLAB showed the dimensions of the matrices when reporting the following error:

??? Error using ==> times

Matrix dimensions must agree.

In my code, this error occurs occasionally due to special cases in my data. As of now, I echo the sizes of the matrices to the screen, which clutters the MATLAB Command Window.

Best Answer

The ability to display the sizes of the matrices involved when reporting the "Matrix dimensions must agree" error is not available in MATLAB.

To work around this issue, either echo the matrix dimensions to the Command Window or enter the following command before executing your code:

dbstop if error

If an error occurs in your code, the MATLAB Debugger starts and you will have access to the matrices that caused the error.

Related Solutions

MATLAB: How to find all the variables of a given class in the MATLAB workspace

A function to find all the variables of a given class is not available in MATLAB.

As a workaround, one can use the following code to display all the variables of class "ClassName" in the Command Window:

s = whos; % Looks for all variables
data_collector = zeros(size(s)); % Pre-allocation
disp('List of ClassName Type variables')
for i = 1:length(s)
    k = s(i).class;
    data_collector(i) = strcmp(k,'ClassName'); 
    if data_collector(i) == 1 % Write variable name in the Command Window
        disp(s(i).name) % Display data
    end
end

Or,

s = whos; 
% find the objects with the type 'ClassName' from the workspace:
matches= strcmp({s.class}, 'ClassName');
my_variables = {s(matches).name}

This also applies to Simulnk Enumeration class. For example:

>> Simulink.defineIntEnumType('a',{'b','c','d'},[1,2,3],'DefaultValue','b','DataScope','Imported','AddClassNameToEnumNames',false) 
>> s = a.b;
>> t = 1;
>> vars = whos;
>> idx = ismember({vars.class}, 'a');
>> vars_double = vars(idx);

Then, "vars_double" will only include the variables "s".

MATLAB: Adding matrices of different dimensions gives an error in MATLAB R2016a and previous releases

Starting with MATLAB R2016b, implicit expansion was updated so that arrays are considered to be compatible sizes if, for every dimension, the dimension sizes of the inputs are either the same or one of them is 1. This allows you to apply element-wise operations and functions to arrays that previously would have caused "matrix dimensions must agree" errors. In this case, starting with MATLAB R2016b, adding a 1x121 matrix to a 121x1 matrix would produce a 121x121 matrix.

More information about how different-sized matrices are operated on since this implicit expansion update can be found in this link:

https://www.mathworks.com/help/matlab/matlab_prog/compatible-array-sizes-for-basic-operations.html

Best Answer

Related Solutions

MATLAB: How to find all the variables of a given class in the MATLAB workspace

MATLAB: Adding matrices of different dimensions gives an error in MATLAB R2016a and previous releases

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