Plotting 3 function using mesh command

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qudsia Bashir 2019-10-10

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https://ww2.mathworks.cn/matlabcentral/answers/484521-plotting-3-function-using-mesh-command

编辑： Alexandra McClernon Ownbey 2019-10-13

I have to plot 3 functions in matlab using mesh command but donot know how to do it please anyone help me?

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Rik 2019-10-10

What is the full text of your homework assignment and what have you tried to find out so far?

qudsia Bashir 2019-10-10

i solved an equation using 3 different method and now i want to plot the results obtained from these three methods.the function is of form u(x,y)

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Answer 1

Alexandra McClernon Ownbey 2019-10-10

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The best way to plot using mesh is to create three 2-D matrices with the same sizes.

x = 0:.1:1;
y = 0:.5:10;
[xq,yq] = meshgrid(x,y);
z = (xq.^2-yq.^2);
figure()
mesh(x,y,z)

Although 'x' and 'y' are different sizes, meshgrid creates a 2-D grid for xq and yq with the m rows and n columns where m equals the length of y and n equals the length of x.

I find the easiest way to think of it is this way:

a 3-D plot needs values for each x, y, and z position. 'xq' is the x coordinates for each point. 'yq' is the y coordinates for each point, and 'z' is the z-coordinates for each respective point. So you create a 2-D grid and give each point some height 'z'.

You do not need to use meshgrid to create your initial 2D matrices, but I find it works well for most cases.

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qudsia Bashir 2019-10-12

i am using the code given below but its giving error that dimmension must agree i have cross check the dimmensions are the same of both functions donot know y this is happening syms x t

for K=1:20

D(1,K)=0 ;

end

for K=1:19

for h=0:19

A(K+1,h+1)=(pi).^(K+2*h);

B(K+1,h+1)=sind(((K+2*h)*180)/2)

D(K+1,h+1)=A(K+1,h+1)*B(K+1,h+1)/(factorial(K)*factorial(h));

end

s=0;

for i=1:18

for j=1:18

x=0.2:0.2:0.8;

s=s+D(i,j).*x.^(i-1).*t.^(j-1);

end

t=0:0.1:0.5;

sia=subs(s,t);

sia1=eval(subs(s,t));

t=0:0.1:0.5;x=(0.2:0.2:0.8)';

exact1 = bsxfun(@times,sin(pi*x),exp(-(pi)^2*t));

B = reshape(exact1',[],1);

exact=B';

errordtm=abs(exact-sia1);

dtmmatrix = vec2mat(sia1,6);

mesh(x,t,exact1,'edgecolor', 'b');

hold on

mesh(x,t,dtmmatrix,'edgecolor', 'r');

legend({'Numerical','Exact'})

hold off

Alexandra McClernon Ownbey 2019-10-13

编辑：Alexandra McClernon Ownbey 2019-10-13

在 MATLAB Online 中打开

the length of your vector 'x' is 4, the length of your vector 't' is 6. just fix these dimensions to match. I suggest using linspace for t using the length of vector x.

I also would suggest initializing D using zeros.

D = zeros(20,1);

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