Solve an equation while we have an if statement that makes the coefficient depends on the variable

I want to solve this

M=166700; %kg%;

g=9.81; %m/s2%;

ro=2500; %kg/m3%;

H=6; %m%;

sigmac=20*(10^6); %Pa%

syms d;

if(d<0.8)

F2=3*(10^6)*(d^2)-30644;

M1=5*(10^7)*(d^2)-552844;

else

F2=103867*(d^2)+(10^6);

M1=2*(10^6)*d^2+2*(10^7);

end

F1=17759*(d^2)+1801.8;

m=sigmac-(M*g/(d^2))-2*ro*H*g+(6*H*F1/(2*(d^3)))+(6*H*F2/(d^3))+(M1*6/(d^3));

fsolve(m,d)

I am not getting an answer because the if test cannot be done without a value for d. Value that I aim to find by this code

[Walter Roberson]

Use piecewise to define F2 and M2. Use vpasolve not fsolve.

Answer 1

[Walter Roberson]

typically the best way to solve these situations is to run both branches separately, vpasolve() each of the branches, test each result to see if it is within the constraints for the branch. There might be several answers.