How to create a for loop in function with a step size as input?

My current function is:

. .

.

x is supposely to run from 765 to 805 with myself individually keying in the step size

X Eg. 765 -> 770 -> 775 -> 780 .... (step size: 5)

      765 -> 767 -> 769 -> 771 .... (step size:2)
      .
      .
      .
      765 -> 765.1 -> 765.2 -> 765.3 (step size:0.1)

.

is repetitive procedure.

So Im thinking of changing X as the input of step size and 765 to 805 already implemented in the function. But Im foreign to the command of for loop.

Anyone can help? Will greatly appreciate it! Thanks!

Answer 1

[Geoff Hayes]

You may be able to avoid the for loop altogether and just pass in a vector of the values from 765 to 805. This should work since your code is already set for element wise operations (due to the presence of the periods). Try the following

 stepSize    = 5;
 x           = 765:stepSize:805;
 y           = 42;
 wavelengths = test(x,y);

We initialize x to be a vector that starts at 765, has a step size of 5, and ends at 805, which is just

 x =

   765   770   775   780   785   790   795   800   805

You should be able to adapt the above for variable step sizes.

[hithere]

Sorry. Do you mean typing this in the command window. Oh the element wise operation is because y is actually a 729x1 variable.

I tried doing this:

.

stepSize = 5;

x = 765:stepSize:805;

[wavelengtha] = test(x,y);

.

But it doesnt work.

.

The error returned was

.

??? Error using ==> minus

Matrix dimensions must agree.

Error in ==> test at 3_

wavelengtha = 1./ ((1./x)-(y/10^7));

[Geoff Hayes]

Since y is a vector (an important fact!) then the above won't work, and so you can use a for loop. You may as well change your function signature to accept the minimum and maximum bounds on x, the step size, and y

 function [wavelengths] = test(minx,maxx,stepx,y)

 % set the x values
 x=minx:stepx:maxx;

 % pre-size wavelengtha
 wavelengths = zeros(size(y,1),length(x));

 for k=1:length(x)
     wavelengths(:,k) = 1./((1./x(k))-(y/10^7));
 end

Then, from the Command Window, call the above function as

 wavelengths = test(765,805,5,y);

[hithere]

thank you so much!