How to enter an if...else...end statement for a dae problem

Question

Urvi 2012-10-1

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/49531-how-to-enter-an-if-else-end-statement-for-a-dae-problem

This is my m file:

*M file* function f=ncs1_dae(t,x)

          %Input parameters
          global alpha A AH AI AO AV ACS beta CPH CPI CPIN CPO CPV dB g hB hI hO hH hV Hmax k M MH min Pset qein R rhol rhov ri ro TIN TR vB lambda;
          input()
          %Variables
          TI=x(1);
........
..........
              =x(16);
          %f(1) to f(6) are ODEs
          f(1)=
          f(2)=
          f(3)=
          f(4)=
          f(5)=
          f(6)=
          %f(7) to f(18) are Algebraic Equations
          f(7)=
          f(8)=
          f(9)=
          f(10)=
          f(11)=
          f(12)=
          f(13)=
          f(14)=
          f(15)=
          f(16)=
          f(17)=
          f(18)=
          f=f';

My question is:

I want to enter if....else statements for a few equations...For example, in f(7), if PV<=Pset, mout = 0 else f(7)=. How can I incorporate that. I need to do this for 5-6 equations. Thanks!

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Urvi 2012-10-3

Please help! its urgent!

Jan 2012-10-3

@Urvi: Please read Answers: Why is your question not urgent.

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Answer 1

Azzi Abdelmalek 2012-10-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/49531-how-to-enter-an-if-else-end-statement-for-a-dae-problem#answer_60744

在 MATLAB Online 中打开

 if PV<=Pset
   mout = 0
 else 
   f(7)=mout-alpha*(PV-Pset)
 end

in general

 if condition1
  % action1
 elseif condition2
  % action2
 elseif condtion n
  % action n
 else
  % action n+1
 end

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Urvi 2012-10-3

I have already tried this but I get an error saying "DAE index appears to be greater than 1".

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Answer 2

Jan 2012-10-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/49531-how-to-enter-an-if-else-end-statement-for-a-dae-problem#answer_60791

The DAE (or ODE) function must be continuous. Therefore IF, MAX, ABS and time-dependent functions are a big DON'T in functions to be integrated. Use event functions instead.

Remember, that the trajectory of an DAE must be kept on a feasible path. Could this be the case, when you insert a discontinuity?