Where is the error in my code?

I am trying to plot three variables Q,R,W using surf function, but I get this error message : Error using surf (line 71)

Z must be a matrix, not a scalar or vector.

Error in time1 (line 13)

surf(R,W,Q)

here is my code that I am trying to run:

r = 0:0.07;

w = 0:4;

[R,W] = meshgrid(r,w);

V1 = @(R,W) -acosh(10*(W./(1600*R + 21))^(1/2))/20000000000

V2 = @(R,W) acosh(10*(W./(1600*R + 21))^(1/2))/20000000000

fun = @(x,R,W)0.0018./((W./((cosh(10^10.*x./0.5)).^2)-(R.*16+0.21)).^0.5);

q = @(R,W) integral(@(x)fun(x,R,W),V1(R,W),V2(R,W));

Q = arrayfun(q,R,W)

surf(R,W,Q)

where is the error, please?

Many thanks

Answer 1

[Voss]

Check the value of r:

r = 0:0.07

r = 0

It is a scalar wth value 0 because the colon operator ":" uses an increment of 1 by default. Since 0.07 - 0 < 1, you get just 0.

Perhaps you meant to use a smaller increment:

r = 0:0.01:0.07

r = 1×8

0 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600 0.0700

Then the rest of the code runs:

w = 0:4;
[R,W] = meshgrid(r,w);
V1 = @(R,W) -acosh(10*(W./(1600*R + 21))^(1/2))/20000000000;
V2 = @(R,W) acosh(10*(W./(1600*R + 21))^(1/2))/20000000000;
fun = @(x,R,W)0.0018./((W./((cosh(10^10.*x./0.5)).^2)-(R.*16+0.21)).^0.5);
q = @(R,W) integral(@(x)fun(x,R,W),V1(R,W),V2(R,W));
Q = arrayfun(q,R,W);
surf(R,W,Q)

[Abdallah Qaswal]

Thank you very much!

It works ! much appreciated!

[Voss]

You're welcome!

Answer 2

[Les Beckham]

You need to specify an increment size if you expect r to be a vector. Currently it is a scalar equal to zero. Q will not be a 2d array if r is a scalar. Thus the error from surf.

r = 0:0.07

r = 0

Maybe you want something like this?

r = 0:0.01:0.07

r = 1×8

0 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600 0.0700

[Abdallah Qaswal]

Thank you!

it works!

Answer 3

[Chris]

The colon operator has a default spacing of 1.

r = 0:0.07

gives:

0,
% next value...
1 > 0.07 % so r = [0]

Use an intermediate step value, if you want:

r = 0:0.01:0.07;

or linspace

[Abdallah Qaswal]

Thank you!

It works now!