Skip to main content
M
MBuck21-Visitor
1-Visitor
September 18, 2011
Solved

Problem with units and odesolve using Mathcad Prime 1.0

  • September 18, 2011
  • 16 replies
  • 16411 views

As recommended by Valery in the previous discussion, I have tried to set up units in a first order heat transfer ODE but am having difficulty with that task. As you can see this I have used various workarounds - first defining the units then stripping the units from variables etc in order to plot the intermediate results. The main problem however, is with the units in the ODE solve block. What I don't understand is why although all units have been explicitly defined in a table at the beginning of the worksheet, nevertheless the ODE reports that the "units are not compatible"? I have tried to explicitly insert the units into the solve block however nothing seems to work. As you can seen from the previous discussion I know this ODE works if you don't have units but I thought one of the big advantages of MathCad Prime 1 was that it can use units in solve blocks. Am I correct in that assertion and if so can someone work out why this error is resulting.

Thanking you in advance.

Kind regards, Mark Buckton

    Best answer by AlanStevens

    Have a look at the attached.

    Alan

    16 replies

    W
    wayne12-Amethyst
    12-Amethyst
    September 18, 2011

    Mark,
    I am not really use to Prime yet, so I might miss something, but:

    You stripped the units from Ts before the solve block, and Tf has units if K, that is one problem.

    Also t is defined as a range variable, to the functions are defined at points only. I did not see an equation for Ts, but it seems you can use that way with range variables; but I don't think that is what you want. Try using t' or tt for range variables for plotting and t for the variable otherwise.

    M
    MBuck21-VisitorAuthor
    1-Visitor
    September 18, 2011

    Wayne;

    Thank you for your suggestion I have tried what you suggested but to no avail.

    Regards, Mark

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    September 18, 2011

    Mark!

    Thanks for use my tip!

    I think you must use units in Cs function too!

    See the picture in attach!

    PS

    I have a dream to rewrite this book for Mathcad Prime with units in ODE

    http://www.springer.com/engineering/computational+intelligence+and+complexity/book/978-3-642-05878-3

    but when I have got Mathcad Prime 7.0

    M
    MBuck21-VisitorAuthor
    1-Visitor
    September 18, 2011

    Valery;

    Thanks for the tip; as you can see it is better but still the ODE refuses to reveal the function for T.s i.e. the steel temperature at a given time due to heat transfer.

    What else am I missing i.e. why are the units incompatible with the ODE solver?

    Regards, Mark

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    September 18, 2011

    See the picture and try please convert to order the right part of the ODE:

    Terms & ConditionsAccessibility statement