Can't solve integrate with unknown value

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Frank Hansper 2016-11-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/313299-can-t-solve-integrate-with-unknown-value

评论： Frank Hansper 2016-11-24

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Im doing calculations in isothermal reactors and need to solve an integral with an unknown value (xa):

My code:

fun = @(xa) ( 1 / (k * CA0^2 * (1 - xa)^2 )
solve ( t == CA0 * integral(fun , 0 , xa ) , xa )

Where t is known, CA0 is known , k is known and xa is my unknown

If I solve by hand I get the right equation:

xa = k*CA0*t / (1 + k*CA0*t)

And can easy find my xa, it is not possible to find the right xa with my code.

Can you get: xa = k*CA0*t / (1 + k*CA0*t) from Matlab or an equation similar, which can find my xa?

Values:

CA0 = 2500, t = 13.57 and k = 1.40 * 10^-4

the xa should be 0.826

采纳的回答

Walter Roberson 2016-11-22

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/313299-can-t-solve-integrate-with-unknown-value#answer_244254

在 MATLAB Online 中打开

syms k CA0 xa t XA 
fun = 1 / (k * CA0^2 * (1 - xa)^2 )
sol = solve(t == int(fun,xa,0,XA), XA, 'ReturnConditions',true)

Then

sol.XA

provided that sol.conditions is true

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Karan Gill 2016-11-23

Frank, regarding "ReturnConditions", did you try looking up the documentation for solve at https://www.mathworks.com/help/symbolic/solve.html ?

Frank Hansper 2016-11-24

Yes and I must say, I had a brain fart - I thought Matlab would return the solution with ''it's'' conditions of the solution. ex. Matlab returns what it uses symbolic and what is uses numeric. So I found it unnecessary at first.

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