Length/Index based if else statements

I have a vector of variable length, for example

b = [0.25;0.5;0.75;1;1.5;1.75;2.0];

and based on the length of this vector, I have some specific parameter K against each element of b, x is the input and my final output is m

if x < b(1)
    m = K(1);
elseif x < b(2)
    m = K(2);
elseif x < b(3)
    m = K(3);
elseif x < b(4)
    m = K(4);
elseif x < b(5)
    m = K(5);
elseif x < b(6)
    m = K(6);
else
    m = K(7);
end

I want to generalize my code based on the length of b. Here, the length was 7 so I had to run it manually like this for 7 elements. How can I generalize this for any length of b?

Answer 1

[Voss]

idx = find(x < b,1);
if isempty(idx)
    idx = numel(b);
end
m = K(idx);

The above assumes b is sorted in ascending order, as in the example. If b is not necessarily sorted, you'd have to sort it first.

[Fawad Khan]

Thank you for your help. I guess this works for me. Although, I don't know why I'm getting an error when using this in MATLAB Function block in SIMULINK. It gives error "compilation of model failed while trying to resolve underspecified signal dimensions"

[Joe Jones]

Dear

Have you solved this problem? I met the error recently.

compilation of model failed while trying to resolve underspecified signal dimensions

@Fawad Farooq Ashraf

[Fawad Khan]

@Joe Jones I guess you have to use the "Ports and Data Manager" for that. In the editor window for MATLAB Function, click on "Edit Data" and then try to specify the type and size. That should work for you.