Using rkfixed in mathcad prime 2.0

Forum|Forum|7 years ago
September 26, 2018
3 replies
9748 views

Greetings!

I want to solve this problem using rkfixed function in mathcad prime 2.0. Help would be highly appreciated!

I am having trouble understanding the derivative matrix of this function

1_vel-and-conc-4.zip

Best answer by LucMeekes

OK I found them (they are there today, they weren't yesterday. I wonder where you grabbed the second from...because both equations define v(z)*x'(z). And I wonder why you use d v(z)/dz on one occasion, and all other derivatives use prime notation: v'(z) and x'(z)...?

Anyway, here goes:

With such results choosing 47, 470 or 4700 steps makes no difference in the graphs.

Possibly not the solution you expected. I suggest you check your differential equations once more.

Success!
Luc

L

LucMeekes

23-Emerald IV

I think first you have to clear up what the function x'(z) is. It is not defined. Do you need to solve two functions ( v and x) simultaneously (which isn't impossible, but requires a set of functions to rkfixed.)?

I suggest you look up the example for "Solving a First-Order ODE Initial Value Problem" in the help. That should explain the usage of rkfixed.

Success!
Luc

A

Asad

Author

1-Visitor

Right! I have two equations which contain v(z), v'(z), x(z) and x'(z)

the rest constants are known

initial conditions are known: v(0)=1; and x(0)=0.013

I need to solve it from ini=0 to end=0.47

I need assistance in forming the derivative matrix. It would be highly appreciated!

Further in the first equation we can assume the value for variable x'(z) as a constant as 0.5 and put the values of v(z) and v'(z) in the second equation to obtain x(z) and x'(z) then iterate the procedure.

I need to use rkfixed to do this.

Thanks!

1_vel-and-conc-4.zip