# Plot two functions with several changing variables

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I want to plot two functions against each other, however I currently have two changing variables (more to be added) however I get a couple error messages I cannot understand:

Matrix dimensions must agree.

Error in Footbridge_2 (line 9)

k = (p.*g + m.*g - n.*(m.*g) - (N-n).*m.*g) ./ -Lext;

Any help would be appreciated

p = 80;

m = 10;

n = 1:1:10;

g = 9.81;

N = 11;

Lext = 68:0.1:80;

L = 68;

k = (p.*g + m.*g - n.*(m.*g) - (N-n).*m.*g) ./ -Lext;

x = sqrt(Lext.^2 - L.^2);

plot(x,k)

xlabel('x')

ylabel('k')

##### 0 Comments

### Answers (3)

KSSV
on 28 Dec 2021

p = 80;

m = 10;

n = 1:1:10;

g = 9.81;

N = 11;

Lext = 68:0.1:80;

L = 68;

[n,Lext] = meshgrid(n,Lext) ;

k = p.*g + m.*g - n.*(m.*g) - (N-n).*(m.*g) ./ -Lext;

x = sqrt(Lext.^2 - L.^2);

plot(x,k)

xlabel('x')

ylabel('k')

##### 1 Comment

the cyclist
on 28 Dec 2021

the cyclist
on 28 Dec 2021

I ran your code inline here. I'm guessing the slightly different error message is due to different MATLAB versions.

The heart of your problem is that you are trying to divide the vector n by the vector Lext, and they have different lengths. A simplified version of what you are attempting is

x = [2 3 5];

y = [7 11];

z = x./y

What does it mean to divide the 3-element vector by the 2-element vector?

You need to figure out what you actually intended to do here.

##### 0 Comments

VBBV
on 28 Dec 2021

p = 80;

m = 10;

n = 1:1:10;

g = 9.81;

N = 11;

Lext = linspace(68,80,length(n));

L = 68;

k = -(p.*g + m.*g - n.*(m.*g) - (N-n).*m.*g) ./ Lext;

x = sqrt(Lext.^2 - L.^2);

plot(x,k)

xlabel('x')

ylabel('k')

Make the vectors equal and plot it.

##### 1 Comment

the cyclist
on 28 Dec 2021

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