Matrix dimensions must agree, Index exceeds matrix dimensions - matlab

Question

I have the following code for positioning some subplots:
fig = figure;
fig.Units = 'centimeters';
fig.Position(3:4) = [25 25];
plotPositions = [ 3, 21, 7, 7;
12, 21, 7, 7;
];
nPlots=length(plotPositions); % shorthand variable for convenience
hAx=zeros(nPlots,1); % preallocate array for axes/subplot handles
for i = 1:length(plotPositions)
plotHandle = subplot(3, 2, i);
plotHandle.Units = 'centimeters';
plotHandle.Position = plotPositions(i,:);
hAx(i)=subplot(3, 2, i);
axis(hAx(i),[ -300 300 0 150]); %
end
If I use
plotPositions = [ 3, 21, 7, 7;
12, 21, 7, 7;
3, 12, 7, 7;
12, 12, 7, 7;
3, 3, 7, 7;
12, 3, 7, 7];
it works, but if use
plotPositions = [ 3, 21, 7, 7;
12, 21, 7, 7;
];
it does not work, and I'm getting the error:
Matrix dimensions must agree.
Index exceeds matrix dimensions.
What's going on?

Answer 1

You shouldn't be using the function length but instead the function size(...,1) to count the rows of plotPositions. length is actually max(size(vec)), which is 6 (number of rows, correctly) in the "working" case, and 4 (number of columns) in the non-working one.
Thus, in the 2nd case you're actually trying to access "nonexistent" rows, so MATLAB complains....