Output argument not assigned during call

I get this error message when I try to run a function that I created. I understand what this is saying, but when I look at my function, the output argument is already correctly defined within the function. So what else could be wrong?

Here is the function:

function y = linInt(xData,yData,x)

if x < xData(1) || x > xData(end)
    error('values in x out of range')
else
    for i = 1:x
        y(i) = yData(i) + ((yData(i+1)-yData(i))*(x-xData(i))/(xData(i+1)-xData(i)));
    end
end
end

Answer 1

[Walter Roberson]

When the code executes, for some reason the statement that assigns a value to the output variable is not being reached. This can happen due to logic errors in how the code was written.

You could post the code for us to examine, or you could use the debugger to trace the flow of the code.

[Walter Roberson]

Your code

for i = 1:x

should be

for i = 1 : length(xData)

Remember, your provided x could be negative.

Answer 2

[Alexandra]

You only assign an output value for y, if the else-branch is executed. You also need to assign a value for y for the if-branch. E.G.

if ...
  y = [];
else 
  y = ...; 
end