Creating a chart of T v. P. How do I use the solve function to solve every part of an array?

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Gabrielle Bartolome 2020-11-11

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https://ww2.mathworks.cn/matlabcentral/answers/643985-creating-a-chart-of-t-v-p-how-do-i-use-the-solve-function-to-solve-every-part-of-an-array

编辑： Setsuna Yuuki. 2020-11-11

I am trying to design a chart of T v. P (torsion v. tension) for a given D(diameter) and a specific n factor of safety) at various values of Sy. The equation that I am using is (sy/(2*n))^2 = ((2*P)/(pi*D^2))^2 + ((16*T)/(pi*D^3))^2

n = 2;
D = 8.35;
start = 10;
finish =200;
sy = 64;
T = linspace(start, finish, 200); 
                syms P;
                eqn = ((2*P)/(pi*D^2))^2 +((16*T)/(pi*D^3)).^2-(sy/(2*n))^2 
                P = solve(eqn, P) %eqn produces an array but it is in a bunch of equations whcih I need to solve. But it doesn't work or put it in an array. 
                tensionValues = eval(P)
                plot(T, tensionValues)

eqn =

P =

Empty sym: 0-by-1

tensionValues =

[]

Error using plot

Vectors must be the same length.

Error in ideasCase1 (line 21)

plot(T, tensionValues)

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Answer 1

Setsuna Yuuki. 2020-11-11

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https://ww2.mathworks.cn/matlabcentral/answers/643985-creating-a-chart-of-t-v-p-how-do-i-use-the-solve-function-to-solve-every-part-of-an-array#answer_540960

编辑：Setsuna Yuuki. 2020-11-11

在 MATLAB Online 中打开

you need use solve() element to element.

n = 2; D = 8.35; start = 10; finish =200;
sy = 64; T = linspace(start, finish, 200); 
syms P;
tensionValues = zeros(1,length(T));
eqn = ((2*P)/(pi*D^2))^2 +((16*T)/(pi*D^3)).^2-(sy/(2*n))^2;
for i = 1:length(T)
p = solve(eqn(i), P); %eqn(1:200)
tensionValues(i) = eval(p(1)); %has two solution, the other solution is p(2)
end
plot(T, tensionValues')