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torme1-Visitor
1-Visitor
January 25, 2018
Solved

Complicated(?) subscript

  • January 25, 2018
  • 3 replies
  • 4153 views

I'm having trouble entering the subscript "n-1" after "prev"  The - 1 doesn't stay with n as part of subscript.

180125 Program.jpgAny suggestions?  I'm using PTC Mathcad Prime 3.1

Best answer by Fred_Kohlhepp

How are you accessing the subscript?  There are two ways to put in a subscript:

  • A literal subscript is part of the variable name, accessed by "cntrl -"
  • A vector or array index subscript, accessed by "["

Capture.PNG

3 replies

V
24-Ruby III
VladimirN24-Ruby III
24-Ruby III
January 25, 2018

Please attach your Mathcad Prime worksheet in archive to the message.

F
Fred_Kohlhepp23-Emerald IAnswer
23-Emerald I
January 25, 2018

How are you accessing the subscript?  There are two ways to put in a subscript:

  • A literal subscript is part of the variable name, accessed by "cntrl -"
  • A vector or array index subscript, accessed by "["

Capture.PNG

    V
    24-Ruby III
    VladimirN24-Ruby III
    24-Ruby III
    January 25, 2018

    After converting?

    W
    Werner_E25-Diamond I
    25-Diamond I
    January 25, 2018

    Guess the variable the derivative is taken wrt can't be a vector element.

    Workaround could be to assign the derivative function to a function func1(prev) and then use that function with the indexed prev[n as argument.

     

    But in Prime you should be able to use the prime symbol ' instead of the derivative operator. Then it should work the way you had set up even with an indexed prev.

     

    EDIT

    I guess I misunderstood your problem in the first place. What you posted works, but your goal is to get rid of the variable prev and use the vector element t_(n-1) directly.

    This also does not work with the Prime operator.

    Bild1.PNG

    As a workaround you could define a local function in your program with the name func'. here the ' is the normal apostrophe, not the Prime symbol from the "operators" menu. On the RHS you either use the prime symbol as shown or the derivative operator you had used.

    Bild2.PNG

     But why would you use a full vector t of values when you only need two variables? You do not return the vector, so it looks like you are not interested in the intermediate approximations.
    Furthermore you may notice, that the precision of root depends on the value of the system variable TOL. If this variable is too high (default is 10^-3) your routine will never stop at t_new = check because check is too inaccurate,
    Bild3.PNG
     
     
     
     
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