How to solve a function with symbolic tool

Question

Davide Bassignana 2017-4-13

0
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https://ww2.mathworks.cn/matlabcentral/answers/335178-how-to-solve-a-function-with-symbolic-tool

编辑： Davide Bassignana 2017-4-13

I want to solve a function with symbolic math toolbox. The equation is quite simple but I can't solve it for the variale I want by hand. It should contain two function handles and one of them contain the variable I want to solve for. Here is the code:

gamma = 1.4;
M0 = 1.5;
PhiD = 0.93;
ed=0.9298;
fM =@ (M) (sqrt(gamma).*M)./(1+0.5*(gamma-1).*M^2)^((gamma+1)/(2*(gamma-1)));
syms M
f = ed*(fM(M)/fM(M0))-PhiD;
Mi=solve(f,M)

Last command returns a 1x1 sym variable and the command window displays : Mi =

 root(487667696955747081*5^(1/2)*7^(1/2)*z^6 + 7315015454336206215*5^(1/2)*7^(1/2)*z^4 + 36575077271681031075*5^(1/2)*7^(1/2)*z^2 - 732792583293936200000*z + 60958462119468385125*5^(1/2)*7^(1/2), z, 1)
 root(487667696955747081*5^(1/2)*7^(1/2)*z^6 + 7315015454336206215*5^(1/2)*7^(1/2)*z^4 + 36575077271681031075*5^(1/2)*7^(1/2)*z^2 - 732792583293936200000*z + 60958462119468385125*5^(1/2)*7^(1/2), z, 2)
 root(487667696955747081*5^(1/2)*7^(1/2)*z^6 + 7315015454336206215*5^(1/2)*7^(1/2)*z^4 + 36575077271681031075*5^(1/2)*7^(1/2)*z^2 - 732792583293936200000*z + 60958462119468385125*5^(1/2)*7^(1/2), z, 3)
 root(487667696955747081*5^(1/2)*7^(1/2)*z^6 + 7315015454336206215*5^(1/2)*7^(1/2)*z^4 + 36575077271681031075*5^(1/2)*7^(1/2)*z^2 - 732792583293936200000*z + 60958462119468385125*5^(1/2)*7^(1/2), z, 4)
 root(487667696955747081*5^(1/2)*7^(1/2)*z^6 + 7315015454336206215*5^(1/2)*7^(1/2)*z^4 + 36575077271681031075*5^(1/2)*7^(1/2)*z^2 - 732792583293936200000*z + 60958462119468385125*5^(1/2)*7^(1/2), z, 5)
 root(487667696955747081*5^(1/2)*7^(1/2)*z^6 + 7315015454336206215*5^(1/2)*7^(1/2)*z^4 + 36575077271681031075*5^(1/2)*7^(1/2)*z^2 - 732792583293936200000*z + 60958462119468385125*5^(1/2)*7^(1/2), z, 6)

But Mi should be a number. How can I fix it ?