14 Replies Latest reply: Feb 16, 2012 4:28 AM by Lilli RSS

    ARGH! Where is my mistake

    Lilli Bronze

      Dear everybody!

       

      You find enclosed my MathCAD file.

       

      My equations depend of THETA, I know by mesure the pressure following THETA.

       

      Why FI"(THETA) isn't a function?

        • Re: ARGH! Where is my mistake
          wayne Gold

          Are the values of Theta in the excell table in degrees?
          If so then assign the degree unit to theta (  theta:=theta*deg) and drop the degree assignments in the functions.

          Mathcad will convert to radians internally, and do computations in radians.

           

          It's a little confusing using angular velocity in radians/s and funcitons that have theta in degrees combined with functions with theta in radians.

          • Re: ARGH! Where is my mistake
            FredKohlhepp Platinum

            The sheet you posted has no data for theta or P(theta); the readfile structuresdon't store the data.  As soon as I create values for theta, all the functions develop values.

            • Re: ARGH! Where is my mistake
              Lilli Bronze

              Thanks all! Unfortunately, the functions don't all develop! If you look your sheet, j"(q) and after doesn't develop, Strangely if I write

              j"(q):=(j'(q)*j'(q)-q)*tanj(q) it's develop, why. It's the same thing after ??????

                • Re: ARGH! Where is my mistake
                  wayne Gold

                  You need to vectorize some of the equations.

                   

                  Mathcad will automatically vectroize, sometimes.  I've see situations where Mathcad appeared to vectorize automatically, because it gave multiple results. But if you then vectorize, the answer is different (and correct).

                   

                  Some of you equations that don't produce multiple results just need to be vectorized, but others should be checked to see if the result when vectorized is the same.

                   

                  You could also put Theta=0..rows()Theta  and P=0..rows(P) at the beginning and it will do the same thing (I did not try though).

                   

                  It also looks like you need to assign units to P,  P=P*psi, or whatever.

                    • Re: ARGH! Where is my mistake
                      Lilli Bronze

                      Hello Wayne,

                      I'm not sure to understand. I added the unit for the P value after your fist respond. I come to solved the problem, I suppresed the excel relation for Theta but now I don't know how to use my pressure.

                      • Re: ARGH! Where is my mistake
                        MikeArmstrong Diamond

                        Mathcad will automatically vectroize, sometimes.  I've see situations where Mathcad appeared to vectorize automatically, because it gave multiple results. But if you then vectorize, the answer is different (and correct).

                        It's a very dangerous situation. I had that happen to me recently. It tends to happen when you have two vectors with one equation.

                         

                        Mike

                    • Re: ARGH! Where is my mistake
                      Lilli Bronze

                      Thanks at all ! Currently, I continue to improve my systeme. I think that is not finish but for the moment the problem are solve.