Use the FUNCTIONINFO structure for registering a custom function with PTC Mathcad. This structure contains information about the name by which PTC Mathcad recognizes the function, the description of the function parameters, its arguments, its return value, and the pointer to the code which executes the function.
Example
FUNCTIONINFO Multiply = { // The function name, as it should appear in Mathcad "Multiply", // The function arguments "a,M", // A brief description of the function "Returns the product of the scalar a and the matrix M",
// The call to your code (LPCFUNCTION)MyCFunctionname;
// The type of the result COMPLEX_ARRAY,
// The number and type of the arguments 2, {COMPLEX_SCALAR, COMPLEX_ARRAY} };