Solving system of equations with conditional statement

Forum|Forum|10 years ago
February 22, 2016
2 replies
4241 views

Hi,

I am just now discovering all that Mathcad can do and I am having trouble with solving a system of equations that includes a conditional statement. If I manually input the statements into the system of equations (at the end), it solves it correctly, but I would like the equations to change based on the selection of LL case. Any help would be appreciated!

Mathcad Question.jpg

Thanks,

Nichole

Other

M

MJG

1-Visitor

I think you need to change your LLcase conditional statements so that they are functions of your three loads. For example:

LLcase.int.LL.and.IM(P.int.LL.truck, P.int.LL.tandem, P.int.LL.lane) := ...

If that doesn't work, please post your worksheet (you can attached files by clicking "use advanced editor").

N

nc-2

Author

1-Visitor

Mark,

Thank you for the response. I'm still unable to get it to work. I'm not that I understand all of the functions in the evlatuation toolbar (and haven't been able to find good examples that show the differences) so maybe I am using the incorrect one.

Thanks,

Nichole

1_Conditional-System-of-Equations-xmcd.zip

T

tietjee

15-Moonstone

The problem may be with the programs. The last line of the program will always be return. You need to change the if statements to:

return x if case = 1

return y if case =2

etc.

1_Truck-xmcd.zip

N

nc-2

Author

1-Visitor

Thanks, David. I'm still missing something....

1_Conditional-System-of-Equations-xmcd.zip

W

Werner_E

25-Diamond I

Mark has correctly suggested that you should use functions and you did it half way right. What you were missing was that you have to use those function in the solve block, too. That means not just the function names but providing the variables you wish to solve for as arguments, too.

Using "return" in every line is not necessary as your cases don't overlap and I don't think that the gain in performance speed is significant. But if you consider it good programming style, you may add those returns again. You may consider adding an "otherwise" line at the end of the functions to provide a value in case LL.case is not an integer in the range of 1 to 5 (0 for instance).

You have three variables you want to solve for, but only two equations. But looking at your cases you always (apart from case 1) have only two variables involved. So Mathcad solves for those two and the third will remain 0 kip.

For LL.case=1 the solve block returns an error as no solution can be found. Thats understandable, because if you look at your equations in that case, you demand Mathcad to find a solution for the "system" consisting of the two equations