How can i modify the matlab built-in function?

supppose i defined a matrix A

how can i modify the inv(A)

[dpb]

Just write your own version and put it in the MATLABPATH before the builtin one.

I DO NOT recommend you do this, however; doing that will not only give you the modified version but may cause other builtin functions that may use inv to use it instead as well and depending upon what modifications are made, either case code to error, run but produce incorrect results, or perhaps run with correct results.

If you have a special case routine that you do need for some purpose, name it uniquely and use it instead, don't mung on built ins -- and particularly numerical routines buried in the bowels of MATLAB.

Answer 1

[Walter Roberson]

Here is the code for inverse. You can modify it as you see fit.

regexprep(char(evalin(symengine, 'expose(symobj::inv)')),'\\n',newline)

ans = 
    'proc(A) : Type::MATLABOutput
       name symobj::inv;
       local result, N;
     begin
       A := symobj::tomatrix(A); 
       if (N := A::dom::matdim(A)[1]) <> A::dom::matdim(A)[2] then
         error(message(\"symbolic:sym:InputMustBeSquare\"))
       end_if; 
       result := 1/A; 
       if result = FAIL then
         result := matrix(N, N, infinity)
       end_if; 
       symobj::standardForm(result)
     end_proc'

[Aleem Ayobami]

Thank you Sir, but i need more information and answers on how to modify the code above.

[Walter Roberson]

Example:

oldsource = char(evalin(symengine, 'expose(symobj::inv)'));
newsource = 'proc(A) : Type::MATLABOutput name symobj::inv; begin error("Never gonna give you up"); end_proc'

newsource = 'proc(A) : Type::MATLABOutput name symobj::inv; begin error("Never gonna give you up"); end_proc'

feval(symengine, 'unprotect', 'symobj')

ans = 

ProtectLevelError

feval(symengine, '_assign', 'symobj::inv', newsource)

ans = 

proc symobj::inv(A) ... end

After which

inv(sym(ones(2,3)))

Error using sym/inv (line 22)
Error in MuPAD command: Never gonna give you up [symobj::inv].

You can see that inv() operating on symbolic objects has been replaced with new source code.