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

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rita richa
rita richa 2022-5-28
回答： Walter Roberson 2022-5-28
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

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回答（1 个）

Walter Roberson
Walter Roberson 2022-5-28
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.

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