Plotting 3 function using mesh command

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qudsia Bashir
qudsia Bashir 2019-10-10
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
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
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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回答（1 个）

Alexandra McClernon Ownbey
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
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
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
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
Alexandra McClernon Ownbey 2019-10-13
编辑：Alexandra McClernon Ownbey 2019-10-13
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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