plotting 2 variables as they change with respect to one another

Question

Joshua Anderson 2021-4-15

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https://ww2.mathworks.cn/matlabcentral/answers/803081-plotting-2-variables-as-they-change-with-respect-to-one-another

编辑： Ahmed Redissi 2021-4-15

I'm trying to plot both A and M and they change simultaneously. If M changes, there is an associated A value within the given ranges. I'm having getting multiple M values to show even though multiple A values are being displayed. Any help would be greatly appreciated.

gamma = 1.4;

%M=1.53

for M= (0.1:0.01:2.19);

for A= (1:0.01:1)

A = 0.5*sqrt((1/M^2)*(2/(gamma+1)*(1+((gamma-1)/2)*M^2))^((gamma+1)/(gamma-1)))

end

plot(A,M)

ylabel('Area')

xlabel('Mach number')

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Answer 1

Star Strider 2021-4-15

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https://ww2.mathworks.cn/matlabcentral/answers/803081-plotting-2-variables-as-they-change-with-respect-to-one-another#answer_676006

编辑：Star Strider 2021-4-15

在 MATLAB Online 中打开

The solution is to subscript ‘A’.

Try this:

gamma = 1.4;
%M=1.53
Mv = (0.1:0.01:2.19);
for k1 = 1:numel(Mv)
    M = Mv(k1);
    A(k1) = 0.5*sqrt((1/M^2)*(2/(gamma+1)*(1+((gamma-1)/2)*M^2))^((gamma+1)/(gamma-1)));
end
figure
plot(Mv,A)
ylabel('Area')
xlabel('Mach number')
grid

However in MATLAB the explicit loop is not necessary, using element-wise operations:

M = 0.1:0.01:2.19;
A = 0.5*sqrt((1./M.^2).*(2/(gamma+1).*(1+((gamma-1)/2).*M.^2)).^((gamma+1)/(gamma-1)));
figure
plot(M,A)
ylabel('Area')
xlabel('Mach number')
grid

This produces the same result as the loop.

See Array vs. Matrix Operations for details.

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Answer 2

Ahmed Redissi 2021-4-15

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https://ww2.mathworks.cn/matlabcentral/answers/803081-plotting-2-variables-as-they-change-with-respect-to-one-another#answer_676011

编辑：Ahmed Redissi 2021-4-15

在 MATLAB Online 中打开

It's not clear why you are iterating over the values of A when you are not using them in the loop. Generaly, you shouldn't iterate over a variable and then change its content inside the loop unless you are incrementing or decrementing.

Does this perhaps solve your issue?

gamma = 1.4;
M = 0.1:0.01:2.19;
A = 0.5*sqrt((1./M.^2).*(2./(gamma+1).*(1+((gamma-1)/2)*M.^2)).^((gamma+1)./(gamma-1)));
plot(M,A)
ylabel('Area')
xlabel('Mach number')