Simulink numerical evaluation to prevent overflow

问题

I have this function

f(a,b) = { 
            a*a/b   if a < b,
            b       if a >= b 
         }

defined for values of a and b between 0 and 1 inclusive.

The function is continuous at all valid values of a and b in this range. (Really! try it yourself!) But I'm not sure how to evaluate it in Simulink. The problem is that I can't figure out how to restate it in a way that I could evaluate both "forks" of the function and take the min or max (e.g. min(a*a,b*b)/b) without having a divide-by-zero error at b=0, and I'd like to avoid getting into things like conditionally-executed subsystems.

Does anyone know how I might go about doing this?

回答1:

You have some strange constraints. Since you insist on evaluating both forks and taking the min of the two, the only solution is to not divide by zero but by a small enough number to avoid an error (eps for instance).

or with if action blocks:

回答2:

I think the simplest approach would be to use a MATLAB function block. You could code it up like this,

function retVal = myfunc(a, b)
   if (a < b)
     retVal = a*a/b;
   else
     retVal = b;
   end
end

This will create a block with 2 inputs and one output. I'm not sure how you are ensuring that a,b \in [0,1], but this will work as long as that restriction is satisfied.

来源：https://stackoverflow.com/questions/10196654/simulink-numerical-evaluation-to-prevent-overflow