MATLAB: How to fix this error

errorfunctionshomework

function [x1, x2] = torus(a,b)
x1= ((.25*pi^2)*(a+b)*((b-a).^2)); 
x2= ((pi^2)*(b^2-a.^2));                  
end
> [volume, area]=torus(0.25:4,a+2)
Error using  * 
Inner matrix dimensions must agree.
Error in torus (line 2)
x1= ((.25*pi^2)*(a+b)*((b-a).^2));

How to go about correcting problem, I thought for the element wise for variables a and b I could just input them as the values for torus(a,b)

Best Answer

Use element-wise multiply operator .* instead of * which is matrix multiply:

x1= ((.25*pi^2)*(a+b).*((b-a).^2)); % <-- changed * to .*
x2= ((pi^2)*(b.^2-a.^2)); % <-- changed ^2 to .^2

Related Solutions

MATLAB: ‘Matrix dimensions must agree error’

You need a mesh to create contour plot

bbfun = @(x1,x2) (4-2.1.*x1.^2+x1.^4/3).*x1.^2 + x1.*x2 + (-4+4*x2.^2) .*x2.^2; 
x1 = -2:1/100:2;
x2 = -1.5:1/100:1.5;
[X1, X2] = meshgrid(x1, x2);
pltvar = bbfun(X1, X2);
contour(X1, X2, pltvar,20)

MATLAB: Can someone help me with these 3D plots

you can plot these shapes in the following two ways(you can choose better way you like):

%%Seashell

[u, v] = meshgrid(linspace(0, 6 * pi, 100), linspace(0, 2 * pi, 100));
x = 2 * (1 - exp(u / (6 * pi))) .* cos(u) .* (cos(0.5 * v))^2;
y = 2 * (-1 + exp(u / (6 * pi))) .* sin(u) .* (cos(0.5 * v))^2;
z = 1 - exp(u / (3 * pi)) - sin(v) + exp(u / (6 * pi)) .* sin(v);
figure, surf(x, y, z), xlabel('x'), ylabel('y'), zlabel('z'), title('Seashell')
%%Eight torus

c = 1;
[u, v] = meshgrid(linspace(-pi, pi, 100));
x = cos(u) .* (c + sin(v) .* cos(u) - sin(2 * v) .* (sin(u) / 2));
y = sin(u) .* (c + sin(v) .* cos(u) - sin(2 * v) .* (sin(u) / 2));
z = sin(u) .* sin(v) + cos(u) .* (sin(2 * v) / 2);
figure, surf(x, y, z), xlabel('x'), ylabel('y'), zlabel('z'), title('Eight torus')
%%Helical spring

r1 = 0.25;
r2 = 0.25;
T = 2;
n = 6;
[u, v] = meshgrid(linspace(0, 2 * n * pi, 100), linspace(0, 2 * pi, 100));
x = (1 - r1 * cos(v)) .* cos(u);
y = (1 - r1 * cos(v)) .* sin(u);
z = r2 * (sin(v) + T * u / pi);
figure, surf(x, y, z), xlabel('x'), ylabel('y'), zlabel('z'), title('Helical spring')
%%Cornucopia

a = 0.3;
b = 0.5;
[u, v] = meshgrid(linspace(0, 2 * pi, 100), linspace(-3, 3, 100));
x = exp(b * v) .* cos(v) + exp(a * v) .* cos(u) .* cos(v);
y = exp(b * v) .* sin(v) + exp(a * v) .* cos(u) .* sin(v);
z = exp(a * v) .* sin(u);
figure, surf(x, y, z), xlabel('x'), ylabel('y'), zlabel('z'), title('Cornucopia')

Or alternatively you can also plot them using ezsurf as follows:

syms u v
%%Seashell
x = 2 * (1 - exp(u / (6 * pi))) * cos(u) * (cos(0.5 * v))^2;
y = 2 * (-1 + exp(u / (6 * pi))) * sin(u) * (cos(0.5 * v))^2;
z = 1 - exp(u / (3 * pi)) - sin(v) + exp(u / (6 * pi)) * sin(v);
figure, ezsurf(x, y, z)
%%Eight torus
c = 1;
x = cos(u) * (c + sin(v) * cos(u) - sin(2 * v) * (sin(u) / 2));
y = sin(u) * (c + sin(v) * cos(u) - sin(2 * v) * (sin(u) / 2));
z = sin(u) * sin(v) + cos(u) * (sin(2 * v) / 2);
figure, ezsurf(x, y, z)
%%Helical spring
r1 = 0.25;
r2 = 0.25;
T = 2;
n = 6;
x = (1 - r1 * cos(v)) .* cos(u);
y = (1 - r1 * cos(v)) .* sin(u);
z = r2 * (sin(v) + T * u / pi);
figure, ezsurf(x, y, z)
%%Cornucopia
a = 0.3;
b =0.5;
x = exp(b * v) .* cos(v) + exp(a * v) .* cos(u) .* cos(v);
y = exp(b * v) .* sin(v) + exp(a * v) .* cos(u) .* sin(v);
z = exp(a * v) .* sin(u);
figure, ezsurf(x, y, z)

I hope it helps. Good luck!

Best Answer

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MATLAB: ‘Matrix dimensions must agree error’

MATLAB: Can someone help me with these 3D plots

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