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AlanStevensAnswer
19-Tanzanite
May 30, 2016

Ok; it took me a while to understand everything, but the attached now has the numerical solution giving (almost) identical results to the symbolic!


I've streamlined the syntax in places.


Alan


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30 replies

LucMeekes23-Emerald V
23-Emerald V
May 30, 2016

Unlike Mathematica (and Maple), Mathcad does not have a built-in facility to solve differential equations symbolically. It only has functions to solve ODE's and PDE's numerically using e.g. odesolve() and pdesolve() respectively.

I have a sheet that will allow to solve a linear ODE, but it only works in Mathcad 11. See here: A classical math problem: differential equations

Your ODE is far from linear. Your only option is to solve it by hand and have Mathcad support you wherever possible.

Success!
Luc

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    WalterSchrabmai12-AmethystAuthor
    12-Amethyst
    May 30, 2016

    Thanks Luc, I have though so and I am afraid that MathCAD can not solve it - neither symbolically nor numerically.

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    AlanStevens19-Tanzanite
    19-Tanzanite
    May 30, 2016

    WALTER SCHRABMAIR wrote:

    Thanks Luc, I have though so and I am afraid that MathCAD can not solve it - neither symbolically nor numerically.

    Not so!  Although Mathcad can't solve it symbolically. it can solve it numerically - when the Solve block is written correctly - see below.

    Also, your explicit model returns 0 (actually, 10^-14) for time 0, even though you pass it an initial value of 333.  It seems your symbolic solution is not of the same equations you have written in the solve block.

    Incidentally, Mathcad has a built-in symbolic LambertW function (though you need to use the float command to get numerical values from it.

    Alan

    LW.PNG

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