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JohnRudnicki15-Moonstone
15-Moonstone
February 11, 2019
Question

System of ODE's

  • February 11, 2019
  • 2 replies
  • 5266 views

I am trying to solve a system of ode's that have gotten increasingly complex as I have added various effects. Everything was working ok until I made the last change (in attached worksheet, addition of the last term - in parentheses - in the expression for dp in the solve block). Now the worksheet does not even get past the solve block to the ode's. I dont get an error message. It just keeps calculating although I have left it for 30 minutes or so. The addition does not seem that complicated: the system is still linear for dv, etc.

Did I do something wrong? Any advice?

2 replies

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-MFra-21-Topaz II
21-Topaz II
February 11, 2019

Hi,

the initialization of the independent variables and the values of some constants, are missing. It must be done before the "Given" instruction. Furthermore, as a rule when using "Odesolve", you should write explicitly the derivatives of the unknown functions  or also using the " ' " .

initialization.jpg

W
Werner_E25-Diamond I
25-Diamond I
February 11, 2019
@-MFra- wrote:

Hi,

the initialization of the independent variables and the values of some constants, are missing. It must be done before the "Given" instruction. Furthermore, as a rule when using "Odesolve", you should write explicitly the derivatives of the unknown functions  or also using the " ' " .

 

He is evaluating the solve block symbolically (which may be the cause for the troubles) and so he does not need any guess values or values for the other variables. After all he needs a symbolic expression in variables for D(t,y)!

And then - unless I'm blind - he is not using a solve block with "odesolve". He uses the commandline solvers to do this job.

 

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-MFra-21-Topaz II
21-Topaz II
February 11, 2019

It seems to me that he is looking for a numerical solution, otherwise why does he define some values like a, b etc.? Regarding "Odesolve", mine is a general advice and not related to the specific problem although, it seems to me, there are differentials like dτ, dθ, etc. and, therefore, the user has somehow transformed the  pde into equations for differentials.

W
Werner_E25-Diamond I
25-Diamond I
February 11, 2019

The calculations sure runs beyond the solve block.

Its the Jacobi calculation which seems to run "endless".

You may speed up the solve block if you delete the commands for clearung the variables mu0 to Lamda for symbolic calculations. As far as I see there is no need to clear those variables.

 

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