Using vpasolve in a for loop ERROR

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Yoslin Herrera on 28 Mar 2019

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Commented: madhan ravi on 28 Mar 2019

I am trying to solve for the variable M given the values of v2. V2 is a 1x100 and I am looking for the value of M given each one of these V2. I tried implementing a for loop but I ended up with a 1x1 M instead of a 1x100.

syms M
M1=1.5;
gamma=1.4;
alpha=linspace(0,13); %theta max is 13 degrees 
%must find M using Prantl-meyer expansion 
v1=sqrt((gamma+1)/(gamma-1))*atan(sqrt((.4/2.4)*(M1^2-1)))-atan(sqrt(M1^2-1));
v1=v1*180/pi;
v2=v1+alpha;
for i =length(v2)
    v2(i)=v1+alpha(i);
    PM=(sqrt((gamma+1)/(gamma-1))*atan(sqrt(((gamma-1)/(gamma+1))*((M^2)-1)))-atan(sqrt((M^2)-1)))*180/pi==v2(i);
    solM(i)=vpasolve(PM,M);
end

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Answer 1

Yasasvi Harish Kumar on 28 Mar 2019

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Hi,

You have an error in your for loop definition and in using vpasolve. I think this should solve it.

syms M
gamma=1.4;
alpha=linspace(0,13); %theta max is 13 degrees
%must find M using Prantl-meyer expansion
v1=sqrt((gamma+1)/(gamma-1))*atan(sqrt((.4/2.4)*(M1^2-1)))-atan(sqrt(M1^2-1));
v1=v1*180/pi;
v2=v1+alpha;
for i =1:length(v2)
    v2(i)=v1+alpha(i);
    PM=(sqrt((gamma+1)/(gamma-1))*atan(sqrt(((gamma-1)/(gamma+1))*((M^2)-1)))-atan(sqrt((M^2)-1)))*180/pi==v2(i);
    solM(i)=vpasolve(PM,M);
end
M = 1.5;
solution = eval(solM);