Why do I get a found an mxArray error pointing to a variable that has a value from a function declared as coder.extrinsic?

Why do I get the error "Expected either a logical, char, int, fi, single, or double. Found an mxArray. MxArrays are returned from calls to the MATLAB interpreter and are not supported inside expressions. They may only be used on the right-hand side of assignments and as arguments to extrinsic functions." for 'index= sum(cummu <= randm) +1;'

Sample code:

coder.extrinsic('get_param');

x = get_param(<modelname/block>,'Value');

y  = x + 5;

Answer 1

[MathWorks Support Team]

You need to explicitly mention the type for the variable that is receiving values from a function declared as coder.extrinsic. If not, MATLAB will return value of type mxArray. 

Sample code's answer:

coder.extrinsic('get_param');

x = double(0);

x = get_param(<modelname/block>,'Value');

y  = x + 5;