Matrix dimensions must agree

I am using Forward Euler to solve based on the given condtions that H'=(S-S(f))/(1-F^2) F^2=(q^2)/(gH^3) S(f)=C(f)F^2 and H(x(1))=H(1).

I am getting the error "Matrix dimensions must agree" for line 17.

What does that mean?

clc; clear all;
h=1000; % step size
xmin=-10000;
xmax=10000;
x=xmin:h:xmax; %x boundaries
n=length(x);
y=zeros(1,n);% Initial condition
x0=0;
q=10;
s=0.00025;
H(1)=30;
Cf=.00200;
g=9.8;
i=1:n-1;
F=sqrt((q^2)/(g*H^3));
s(i+1)=Cf*(F);
dH=(s-s(i+1))/((1-F));
for i=1:n-1
    x(i+1)=i*h;
    y(i+1)=y(i)+h*dH;
end
figure
hold on
plot (x,y,'r', 'linewidth',2)
xlabel ('Channel Distance(m)')
ylabel ('Water Elevation(m)')
title ('Water Elevation vs Channel Distance')

[Star Strider]

If you separately query ‘s’ and ‘s(i+1)’, you will find that ‘s’ is a (1x20) vector, and ‘s(i+1)’ is a (1x20) vector.

You have to determine how best to deal with that.

[Star Strider]

Kolleggerm1’s Answers moved here —

First:

h=1000;
xmin=-10000;
xmax=10000;
x=xmin:h:xmax;
n=length(x);
H=zeros(1,n);
x0=0;
q=10;
s=0.00025;
H(1)=30;
Cf=.00200;
g=9.81;
i=1:n-1;
slope=(s-(Cf(q.^2)/(g(H(i).^3))))/(1-((q.^2)/(g(H(i).^3))));
for i=1:n-1
    x(i+1)=x(i)-h;
    H=H(i-1)-slope*h;
end
figure
hold on
plot (x,H,'r', 'linewidth',2)
xlabel ('Channel Distance(m)')
ylabel ('Water Elevation(m)')
title ('Water Elevation vs Channel Distance')

Second:

I was able to fix the original error and am now getting this one (for the above code)

Index exceeds the number of array elements (1).

Error in Alltogether (line 15)

slope=(s-(Cf(q.^2)/(g(H(i).^3))))/(1-((q.^2)/(g(H(i).^3))));

[Star Strider]

You are missing a number of (probably multiplication) operators here:

slope=(s-(Cf(q.^2)/(g(H(i).^3))))/(1-((q.^2)/(g(H(i).^3))));

I used this:

slope=(s-(Cf*(q.^2)./(g*(H(i).^3))))./(1-((q.^2)./(g*(H(i).^3))));

that eliminated that error, however your code now has others with respect to ‘x’ and ‘H’ not having equal lengths in the plot call.