MATLAB Central Newsreader - strange error message

strange error message

stpatryck — Mon, 14 Sep 2009 08:03:02 -0400

Hello Folks,

I typed in these commands:
>> t=0:0.01:2*pi;s=t;
>> x=cos(t).*cos(s);y=cos(t).*sin(s);z=sin(t);
>> surf(x,y,z)

I got the following error message:

??? Error using ==> surf at 78
Z must be a matrix, not a scalar or vector.

What am I doing wrong???

Re: strange error message

James Tursa — Mon, 14 Sep 2009 08:22:02 -0400

stpatryck <stpatryck@gmail.com> wrote in message <ec15a73f-76ad-4291-a568-b615d121e464@v36g2000yqv.googlegroups.com>...
> Hello Folks,
>
> I typed in these commands:
> >> t=0:0.01:2*pi;s=t;
> >> x=cos(t).*cos(s);y=cos(t).*sin(s);z=sin(t);
> >> surf(x,y,z)
>
> I got the following error message:
>
> ??? Error using ==> surf at 78
> Z must be a matrix, not a scalar or vector.
>
>
> What am I doing wrong???

Amazingly enough, the error message means exactly what it says! Your x and y inputs to surf form a mesh, and z forms the height at each mesh point. i.e., each combination of an x element and a y element needs to have a z element. So if x is an n-vector and y is an m-vector, then Z needs to be a m-by-n matrix.

James Tursa

Re: strange error message

SaintPatrick — Fri, 18 Sep 2009 03:11:58 -0400

On Sep 14, 4:22 am, "James Tursa"
<aclassyguy_with_a_k_not_...@hotmail.com> wrote:
> stpatryck <stpatr...@gmail.com> wrote in message <ec15a73f-76ad-4291-a568-b615d121e...@v36g2000yqv.googlegroups.com>...
> > Hello Folks,
>
> > I typed in these commands:
> > >> t=0:0.01:2*pi;s=t;
> > >> x=cos(t).*cos(s);y=cos(t).*sin(s);z=sin(t);
> > >> surf(x,y,z)
>
> > I got the following error message:
>
> > ??? Error using ==> surf at 78
> > Z must be a matrix, not a scalar or vector.
>
> > What am I doing wrong???
>
> Amazingly enough, the error message means exactly what it says! Your x and y inputs to surf form a mesh, and z forms the height at each mesh point. i.e., each combination of an x element and a y element needs to have a z element. So if x is an n-vector and y is an m-vector, then Z needs to be a m-by-n matrix.
>
> James Tursa

I don't understand -- z shows up in the workspace as a matrix with the
same dimensions as x and y. Since t is a matrix, z = sin(t) should
also be a matrix.

Re: strange error message

James Tursa — Fri, 18 Sep 2009 05:01:04 -0400

SaintPatrick <patrickmyu@gmail.com> wrote in message <45341af6-364d-45e0-bcc2-3536c8ae52fe@g6g2000vbr.googlegroups.com>...
>
> I don't understand -- z shows up in the workspace as a matrix with the
> same dimensions as x and y. Since t is a matrix, z = sin(t) should
> also be a matrix.

>> t=0:0.01:2*pi;s=t;
>> x=cos(t).*cos(s);y=cos(t).*sin(s);z=sin(t);
>> whos
  Name Size Bytes Class
  s 1x629 5032 double array
  t 1x629 5032 double array
  x 1x629 5032 double array
  y 1x629 5032 double array
  z 1x629 5032 double array

So why do you think t and z should be matrices? Clearly t is a vector, and z is a vector also because it is sin of a vector.

James Tursa

Re: strange error message

stpatryck — Sun, 20 Sep 2009 21:49:31 -0400

On Sep 18, 1:01 am, "James Tursa"
<aclassyguy_with_a_k_not_...@hotmail.com> wrote:
> SaintPatrick <patrick...@gmail.com> wrote in message <45341af6-364d-45e0-bcc2-3536c8ae5...@g6g2000vbr.googlegroups.com>...
>
> > I don't understand -- z shows up in the workspace as a matrix with the
> > same dimensions as x and y. Since t is a matrix, z = sin(t) should
> > also be a matrix.
> >> t=0:0.01:2*pi;s=t;
> >> x=cos(t).*cos(s);y=cos(t).*sin(s);z=sin(t);
> >> whos
>
> Name Size Bytes Class
> s 1x629 5032 double array
> t 1x629 5032 double array
> x 1x629 5032 double array
> y 1x629 5032 double array
> z 1x629 5032 double array
>
> So why do you think t and z should be matrices? Clearly t is a vector, and z is a vector also because it is sin of a vector.
>
> James Tursa

Sorry, my bad, I meant "vector" instead of matrix. I should have been
more specific. A vector is a 1 x n or n x 1 matrix. (Feel free to
correct me if I'm mistaken.)

Nevertheless, all of the variables have the same dimensions, so why
the error message?

t=0:0.01:2*pi;s=t;
x=cos(t).*cos(s);y=cos(t).*sin(s);z=sin(t);
surf(x,y,z)

??? Error using ==> surf at 78
Z must be a matrix, not a scalar or vector.

Patrick

Re: strange error message

Matt Fig — Sun, 20 Sep 2009 22:04:01 -0400

stpatryck <stpatryck@gmail.com> wrote in message <02e88d83-1feb-
> Nevertheless, all of the variables have the same dimensions, so why
> the error message?

You are not listening either to us or MATLAB. The criteria is NOT that the variables have the same dimensions! Is THAT what the error message says? No. Read it again, and read the doc for surf, there is an example in the documentation. Copy and paste the example, then look at the output from whos.

doc surf % READ IT.

Re: strange error message

Tom — Fri, 16 Oct 2009 21:06:03 -0400

"Matt Fig" <spamanon@yahoo.com> wrote in message <h968sh$evd$1@fred.mathworks.com>...
> stpatryck <stpatryck@gmail.com> wrote in message <02e88d83-1feb-
> > Nevertheless, all of the variables have the same dimensions, so why
> > the error message?
>
>
>
> You are not listening either to us or MATLAB. The criteria is NOT that the variables have the same dimensions! Is THAT what the error message says? No. Read it again, and read the doc for surf, there is an example in the documentation. Copy and paste the example, then look at the output from whos.
>
> doc surf % READ IT.

I'm surprised by the lack of empathy in these replies. Isn't this a help forum? Why scan and post answers to threads asking for help, but make the asker feel like an idiot with replies like "READ IT" or "amazingly, just what it says!"?? Clearly MATLAB isn't as easy as you make it out to be if there's a site devoted to answering questions about the product!!!

It's unfortunate if you both were made to feel inferior during your formative education if you asked a question someone else perceived as remedial. But get over it and show others who know less some courtesy.

Re: strange error message

dpb — Fri, 16 Oct 2009 23:10:30 -0400

Tom wrote:
> "Matt Fig" <spamanon@yahoo.com> wrote in message
> <h968sh$evd$1@fred.mathworks.com>...
>> stpatryck <stpatryck@gmail.com> wrote in message <02e88d83-1feb-
>>> Nevertheless, all of the variables have the same dimensions, so
>>> why the error message?
>>
>>
>> You are not listening either to us or MATLAB. The criteria is NOT
>> that the variables have the same dimensions! Is THAT what the
>> error message says? No. Read it again, and read the doc for surf,
>> there is an example in the documentation. Copy and paste the
>> example, then look at the output from whos.
>>
>> doc surf % READ IT.
>
> I'm surprised by the lack of empathy in these replies. Isn't this a
> help forum? Why scan and post answers to threads asking for help,
> but make the asker feel like an idiot with replies like "READ IT" or
> "amazingly, just what it says!"?? Clearly MATLAB isn't as easy as
> you make it out to be if there's a site devoted to answering
> questions about the product!!!
...
Well, the very first response told OP _exactly_ what was wrong and
included the needed dimensions.

c.s-s.m culture is pretty much a "help to learn" mentality as opposed to
force-feed. It's expected the learner/asker will do their part, too,
and there seems to be a certain lack here of following direction.

OP--

ML means a 2D array when it says "matrix" and explicitly notes that a
vector isn't. An [nx1] (or [1xn]) doesn't qualify, either even though
there are 2-dimensions; it must be mxn of the vector size.

see meshgrid

--

Re: strange error message

Matt Fig — Mon, 19 Oct 2009 16:55:19 -0400

"Tom " <slustu7@gmail.com> wrote in message
> I'm surprised by the lack of empathy in these replies. Isn't this a help forum? Why scan and post answers to threads asking for help, but make the asker feel like an idiot with replies like "READ IT" or "amazingly, just what it says!"?? Clearly MATLAB isn't as easy as you make it out to be if there's a site devoted to answering questions about the product!!!

There is a difference between a lack of empathy and exasperation. The OP was told exactly what the problem was, by other posters and MATLAB itself. The fact that the OP wasn't getting this point is why I said, "READ IT."
You see, this is emphasis is not derision. When someone doesn't get something, you emphasize the important part for them.