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Problems using the MINIMIZE function

Problems using the MINIMIZE function

I have an optimisation problem which I am having trouble with.

Would someone be able to tell me if I have set up the solve block incorrectly?

Can mathcad solve for more than one Objective Function? If so, how?

I have attached a copy of my problem, and would appreciate any help that could be offered.
9 REPLIES 9

Problems using the MINIMIZE function

Hi!
I try to help You.
1. What is it $:=kg^0.8*m^2.6/s^1.6
We can use $:=cd for inserting in sheet currency (see my messages in Economic & Finance miniforum).
2. I think COST(H, T.max):=((H/m)^1.8*(T.max/N)^0.8)*$
3. Guess value must be just higher Given key-word.
Good Luck!
Valery Ochkov
http://twt.mpei.ac.ru/ochkov

Problems using the MINIMIZE function

Hi, thanks for your help!

1. $:=kg^0.8*m^2.6/s^1.6 is a definition I used to get the answer in $.
2. Your method to convert the answer to $ is much better.
3. Can mathcad minimize a system of equations, or can it only minimize a single equation and its variables?

I have a series of equations which give me the values of H and T.max. Mathcad only seems to optimise the single equation, ie
COST(H, T.max):=((H/m)^1.8*(T.max/N)^0.8)*$
I need it to optimise a system of equations to give the minimum value of COST.

Problems using the MINIMIZE function

Hi,
We can directly optimize in Mathcad only a function.
It is not clear what you mean under optimization a system of equations.
Valery Ochkov
http://twt.mpei.ac.ru/ochkov

Using the Minimie function with two Variable

Hi again!
If the task of linear (or nonlinear) programming has only two unknown values (educational or "children" tasks), its numerical solution is expedient for anticipating by the graphic solution.
Tip # 22 from the book "Tips for Mathcad users"
http://twt.mpei.ac.ru/ochkov/Sovet_MC/index.htm
See attach
Valery Ochkov
http://twt.mpei.ac.ru/ochkov

Using the Minimie function with two Variable

The equation I wish to optimise has two variables, however these two variables are defined by several equations. Taking your "optimum plan of manufacture" for example, where:

Say we have Variables:
A,u,z,C

Equation to be optimised:
COST(x,y):=8x+12y

Where:
x:=A*cosh(z/A)+C
and
y:=u*A

Given:
2x+4y<=440, 0.5x+0.25y<=65, 2x+2.5y<=320

How do I find optimum value of A,u,z, and C to give a minimum value of COST?

Using the Minimize function with 4 Variable

I think You must do so:

COST(A,u,z,C):=8*(A*cosh(z/A)+C)+12*u*A


A:=? u:=? z:=? C:=?


Given
2*(A*cosh(z/A)+C)+4*u*A<=440
0.5*(A*cosh(z/A)+C)+0.25*u*A<=65
2*(A*cosh(z/A)+C)+2.5*u*A<=320
Minimize(COST,A,u,z,C)=Answer

Valery Ochkov
http://twt.mpei.ac.ru/ochkov

Using the Minimize function with 4 Variable

Valery,

If I have one function that is dependant on 5 or more other functions, then it becomes too cumbersome to use substitution (maybe the Solving and Optimisation Extension Pack fixes this issue).

I have solved this problem using MS Excel's Sover tool. I am disappointed to find that mathcad is not capable of solving the same problem.

I have attached the excel spreadsheet for to show how easy it was...and how easy it should have been in Mathcad.

If you wish to watch Excel in action, change the values of the variables A, Xo, and C, then run Solver (the constraints should already be set).

None the less , I appreciate all of the assistance you have given this Mathcad Newbie.

Kind Regards,
Mathew Moore.

Using the Minimize

Hi!
I see you problem but sorry - no time to correct your sheets. I will take your task my student.
Solvers in Mathcad and in Excel was made one firm Frontline Systems, Inc.
Difference:
In Excel we can use integer solutions
In Mathcad we can use units
See now for help:

Valery Ochkov
http://twt.mpei.ac.ru/ochkov

Using the Minimize function with 4 Variable

Probably not of great interest to the original poster any more, but still a good example. It's quite simple once you keep track of what is a function of what. In XL cells are implicit functions of other values, as referenced. In Mathcad values are just values, and functions must be explicit.

Tom Gutman
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