Does the order of the equations in a coupled OIDENT solver matter?

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My code runs, however, if i change the order of the equations defined in my formula my graphs changes as well. Can somebody tell me why this is? Now i do not know what the right

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  • 2021-01-28 15:21

    In the second code snippet you are referring to e.g. u_1 before you assign it. The same goes for u_2 ... u_4. So whatever the values of those are before the assignments get used in the calculations for du1dt...duddt

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  • 2021-01-28 15:38

    In the code block

         u_1 = (L_L*u_s + w_L*u_2)/w_L
         u_2 = (w_d*u_d)/w_L
         u_3 = (w_L*u_2)/w_r
         u_4 = (L_r*u_s + w_r*u_3)/w_r
         u_d = (w_r*u_3)/w_d
    

    you change all the u values. Of course it makes a difference in the function if you compute further values with the modified or unmodified u values.

    The easiest thing to do is not to re-use these variable names. Change u to v on the left side and then check whether in uses further down you really wanted to use the modified v value or the u value. Your original code with that change would be

         v_1 = (L_L*u_s + w_L*u_2)/w_L
         v_2 = (w_d*u_d)/w_L
         v_3 = (w_L*v_2)/w_r
         v_4 = (L_r*u_s + w_r*v_3)/w_r
         v_d = (w_r*v_3)/w_d
    
         du1dt =  - g*((p_2-p_1)/L_L + deltap_L/L_L) - b_L*v_1 
         du2dt =  - g*((p_2-p_1)/L_L - deltap_L/L_L) - b_L*v_2
         du3dt =  - g*((p_4-p_3)/L_r - deltap_R/L_r) - b_R*v_3
         du4dt =  - g*((p_4-p_3)/L_r + deltap_R/L_r) - b_R*v_4
         duddt =  - g*((p_3-p_2)/L_d) - b_D *v_d
    
    
    
    
         dp1dt =  - v_1
         dp2dt =  - v_1
         dp3dt = + v_4
         dp4dt = + v_4
         ddeltap_Ldt =  - v_1
         ddeltap_Rdt =  v_4 
    
    

    Now any re-arrangement of the indicated type will cause an error that some variable used on some right side was not previously defined.

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