code/solution for integration with respect in time in matlab

Question

siti khadijah 2016-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/285629-code-solution-for-integration-with-respect-in-time-in-matlab

回答： Steven Lord 2016-5-24

Hai fellow friends,

I have a question regarding the integration with respect to time. I have a simple equation as follow:

 tau = theta1_dd(t)*((m1 + m2)*L1^2 + I1) + L1*g*sin(theta1(t))*(m1 + m2) + L1*L2*m2*theta2_dd(t)*cos(theta1(t) - theta2(t)) + L1*L2*m2*sin(theta1(t) - theta2(t))*theta2_d(t)
               theta2_dd(t)*(m2*L2^2 + I2) + L2*g*m2*sin(theta2(t)) + L1*L2*m2*theta1_dd(t)*cos(theta1(t) - theta2(t)) - L1*L2*m2*sin(theta1(t) - theta2(t))*theta1_d(t)

I tried using int (tau). However, the result was integrated with thetas' not with time. Could anyone here help me regarding this issue? thanks :)

Regards, Siti

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Answer 1

Steven Lord 2016-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/285629-code-solution-for-integration-with-respect-in-time-in-matlab#answer_223285

From the documentation for int:

"int(expr,var) computes the indefinite integral of expr with respect to the symbolic scalar variable var. Specifying the variable var is optional. If you do not specify it, int uses the default variable determined by symvar."

So specify var, the variable with which you want expr to be integrated, in your int call.