# Bug in Matlab 7? why does this happen--scalar division or vector division?

Discussion in 'MATLAB' started by kiki, Oct 28, 2004.

1. ### kikiGuest

Dear all,

I want to see the plot of "z/w" where "z" and "w" are defined as follows:

y=[-10:0.1:10];
z=((normcdf(1-y, 0, 1)-normcdf(-y, 0, 1))-(normcdf(-y, 0, 1)-normcdf(-1-y,
0, 1)));
w=normcdf(1-y, 0, 1)-normcdf(-1-y, 0, 1);

% 1)

plot(y, z/w)

% I got a result which is zero everywhere on the plot...

% 2)

plot(y, z./w)

% I got a non-zero plot which is the correct one...

I understand now that the second one is correct, since z and w are vectors,
so I should use element-wise division.

The problem is that I don't understand why in the first approach that the
"plot(y, z/w)" generates a zero-result plot?

In my understanding, if the vector over vector does not abide by the syntax,
the Matlab syntax check should raise an error saying "subscript
mismatch...".

But this time it did not raise any error so I had been wasting a lot of time
by assuming the zero-results were correct...

So why "z/w" (z and w are non-zero, but zero at only some points) gives zero
results?

Thanks a lot

kiki, Oct 28, 2004

2. ### the cyclistGuest

kiki wrote:

"z/w" is a valid matrix division, albeit a little beyond my
understanding for vectors rather than matrices. See "help slash" for
how it is defined.

the cyclist, Oct 28, 2004