Cannot use input value with 'numerictype' in MATLAB Fcn

The code below works fine

function y = fcn(u)
word_length = u.WordLength;
bin_pt = 5;
T = numerictype(1,word_length, bin_pt);
y = reinterpretcast(u,T);

But I want user-defined binary point and when I take it as an input (from a mask variable or a constant) it doesn't

function y = fcn(u, bin_pt)
word_length = u.WordLength;
% bin_pt = 5;
T = numerictype(1,word_length, bin_pt);
y = reinterpretcast(u,T);

This gives the following error

Answer 1

[Walter Roberson]

Every signal in Simulink must be of specific type, and fixed point values of different length are considered different data types. The consistency checking is done at the time the model is to be built, but the building process compiles in specific internal routines and lengths.

Options include:

• Permitting your user to choose only one of a limited number of widths and build distinct subsystems for every permitted width that hold all of the blocks that need to know about that width, with the block boundaries at the point where the computations no longer rely upon the width;
• Variant controls https://www.mathworks.com/help/simulink/ug/switching-between-variants.html
• there might be options about busses that carry around the length and an array of bytes and then at each point you switch on the length to choose the appropriate instruction and push the results back into a bus again.

[M. Saad]

Unforunately, multiple variants strategy doesn't seem to be possible in my case at the moment. I tried many workarounds but still no success. The 'numerictype' is extremely inflexible when using embedded MATLAB function.

I simply want to implement the functionality of 'reinterpretcast' in Simulink (only need to modify signedness and the binary point, word length remains the same). Could you suggest anything in this regard?

[Walter Roberson]

function y = fcn(u)
switch u.WordLength
    case 1
        T = numerictype(1, 1, 5);
    case 2
        T = numerictype(1, 2, 5);
    case 3
        T = numerictype(1, 3, 5);
    case 4
        T = numerictype(1, 4, 5);
    case list off all of the other user possibilities individually
end
y = reinterpretcast(u,T);

[M. Saad]

I think I couldn't make myself clear, my case was otherwise. However, I have solved it as following, might it help someone.

I used Data Type Propagation block with a Data Type Conversion block. Input is at Ref 1 to keep the number of bits same and Ref 2 is provided by the constant block whose signedness and binary point I can modify according to the user input. In Data Type Propagation block one can parameterize which things to change from which references.