# Passing array to a function

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Tom on 8 Mar 2011
Hi,
I'm getting an error message when attempting to pass some variables (including arrays), and can't figure out why.
Here is my code..
frequency(x) = getFreq(ts, Rdata, Ldata, foot);
Ldata is a 819x3 double, Rdata is a 1362x3 double, foot=1, ts=10959
On the function side, the parameters are
function Freq = getFreq(timestamp, SessionL, SessionR, foot)
The error message I'm getting is
??? In an assignment A(I) = B, the number of elements in B and I must be the same.
Error in ==> main at 71 frequency(x) = getFreq(ts, Rdata, Ldata, foot);
Thanks

Teja Muppirala on 8 Mar 2011
Whatever Freq is when you exit the function getFreq, it is not of a size compatible with the index vector x.
For example, this will also give you the same error.
A = [0 0 0];
x = [1 3];
A(x) = sum( rand(3) )
This fails because x only has two values, but the sum returns a vector of 3 values. This, however, is OK:
A = [0 0 0];
x = [1 3];
A(x) = sum( [1 2; 3 4] )
So just go make sure that the value getting returned (Freq) is of a proper size to match with x.
Try the following:
temp = getFreq(ts, Rdata, Ldata, foot);
size(temp)
size(x)
and compare what you get. That should help you see why it's not working.

Brett Shoelson on 8 Mar 2011
You'll need to show us a bit more. It would be particularly useful, for instance, to see line 71 of getFreq.
Consider putting a breakpoint there and re-running. Are the variables what you expect when you get to that point? If so, you have a logical flaw in your code. If not, trace backward and figure out how/why something got changed.
Brett
Tom on 8 Mar 2011
sorry i should have stated, line 71 is the first line shown, the line calling the function. The variables are how i expected, I just cant understand why that type of error would occur

Matt Tearle on 8 Mar 2011
What Teja said.
I hate to ask the dumb question, but do you actually want to do indexing on line 71? Many people write things like foo(x) = ... because they're used to thinking in mathematical terms (foo is a function of x). But [voice = Morbo] "MATLAB does not work that way" [/voice]. In MATLAB, foo(x) = ... means "calculate the RHS (...) and put the result into the elements of foo indexed by x". So the fundamental dumb question to ask is: are you really trying to save the output from getFreq into a subset of the variable frequency, in which case do what Teja said to check dimensions, or are you actually just trying to save the output of getFreq to a variable called frequency, in which case get rid of the (x).
Matt Tearle on 8 Mar 2011
Er, just to clarify: "dumb" question not because *you're* being dumb, but because *I* feel dumb asking, when it's entirely possible that, yes, you do want to do that.

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