Hi all, i try to use interp1 function. but i have two data input (Y), the values of the underlying function , one of them is a vector while the other is constant value. so how i can deal with Y

yi = c(x,Y,xi)

[Stephen23]

What is c? Please show us what values you have, and how you want to use them.

Answer 1

[John D'Errico]

So, what you are telling us is, that you apparently have a "function" Y(x), such that for ANY point x, the value of the function Y(x) is Y, a constant. You wish to interpolate that "function"?

My question is, why bother? You already know the function is constant. So the simple answer is to use repmat, which will return the same constant value for every value of xi.

yi = repmat(Y,size(xi));

The only thing I am unsure about is what you intended by the code fragment:

yi = c(x,Y,xi)

This is what Stephen also referred to. I see that this call seems to be identical to the format interp1 uses. And you refer to interp1 in your question. Therefore, I assume that you are asking what function can be used to interpolate a constant function. Again, the answer is, no special function is required, perhaps beyond something trivial like repmat.

[Muna Shehan]

Thank you for your response, I am tired to prepare simulation input for a dynamic model which is subjected to the equation xdot= A.x+B.u, where A & B are matrices with constant elements xdot is the time derivative for the state variables vector and u is the input vector with two elements one of them change with time while the other one is constant. My question is : can i use interp1 function with this dynamic model.

[Muna Shehan]

where Y is a matrix that should contain the input of u (2xlength(x). So how i can write Y if it contains two inputs one of them is vary with time and the other is constant yi = interp1(x,Y,xi)

[Jonathan Hawkins]

As to "Why bother..." I've run into this problem when I'm writing code that needs to interpolate for a generic function, which can be constant.

It's incredibly irritating that interp1 throws an error if the function you're interpolating happens to be constant. That's just shoddy design on Mathworks' part if you ask me.