MATLAB: Undefined function or variable k symsum

kSymbolic Math Toolboxsymssymsumundefinedvariable

Why am I receiving an error when using the "symsum" function?

error: Undefined function or variable 'k'.

Best Answer

This error is because the symbolic variable, 'k', needs to be created before using this function.

>> syms k

Related Solutions

MATLAB: ‘Not convertible to floating-point’ error when using min() with symbolic variables

The reason of the error is that the input arguments to "min" are not "convertible to floating-point numbers" as "xx" is a symbolic variable. To avoid the error, one could wrap the call to "min" in another symbolic function such that "xx" is conceivably reduced to a floating number. Here is the code that does that:

xx = sym('xx','real') ;
symmin = @(x,y)feval(symengine,'min',x,y);
LambdaCC = symfun(sqrt(1-2*symmin(xx,1/2)), xx);

Also, the link below might be helpful as well:

https://stackoverflow.com/questions/29527592/matlab-using-a-minimum-function-within-symsum

MATLAB: Symsum is slow

"symsum" is the wrong function to use if you want to add up a few terms. It spends time to look for a general formula that is valid for arbitrarily many terms, and then applies that formula to the given number of terms.

"symsum" is much better when there are many terms.

For fewer terms, use the "sum" function:

>> tic; p = sum(subs(fun(k),k,(-1:1)')); toc; % about 1 second

Please see the following link for more information:

https://www.mathworks.com/help/releases/R2019a/symbolic/symbolic-summation.html#buw9day-1

Best Answer

Related Solutions

MATLAB: ‘Not convertible to floating-point’ error when using min() with symbolic variables

MATLAB: Symsum is slow

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