MATLAB: Matlabfunction generates redundant copies of variables

functionmatlabfunctionoptimizerepeatslowsymbolicSymbolic Math Toolboxvariables

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The reason why it is slow and creating all those variables is because 'Optimize' is set to true by default. This analysis can be very costly so setting 'Optimize' to false will resolve this issue.

>> matlabFunction(symbfunc, 'File', fileName, 'Optimize', false);

Please note that while having Optimize set to true does create redundant variables, the duplication should not affect the performance of the generated C++ code.

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MATLAB: How to create a vector function from a symbolic expression

The "matlabFunction" function allows you to specify the desired input arguments using the "Vars" option. The following example will generate the desired function:

>> syms a b c 
>> symExp = a .* b + c;
>> vectorFcn = matlabFunction(symExp, 'Vars', {symvar(symExp)});

The "symvar" function takes a symbolic expression and returns an array of the symbolic variables use in that expression in alphabetical order.

This array is then placed in a cell array when specifying the input arguments to the generated function. This indicates that the specified arguments are meant to be passed as a single vector.

The newly generated function can be called as follows:

>> vectorFcn([1 2 3])
ans = 
     5

This method will work for any symbolic expression. However, remember that the order of elements in the vector must correspond to the symbolic variables of the expression in alphabetical order.

If instead you would like to directly specify an order, you can simply replace the call to "symvar" with an array of symbolic variables:

>> vectorFcn = matlabFunction(symExp, 'Vars', {[a b c]});

This gives you more freedom, but you will have to change the array if different symbolic variables are used.

MATLAB: Is fplot empty while ezplot works on imaginary inputs

The reason why the plot is not showing up is due to the imaginary part of "sol". The "ezplot" function ignores the imaginary part and just plots the real part. This happens to be good in this case, but is not a good method for all scenarios. For this reason, the "fplot" function simply leaves out parts of a function plot that are not real.

In order to get the desired plot, simply grab the real part of "sol".

>> fplot(real(sol))

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Related Solutions

MATLAB: How to create a vector function from a symbolic expression

MATLAB: Is fplot empty while ezplot works on imaginary inputs

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