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Solving equations with changing 1 variable

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Level 5

Solving equations with changing 1 variable

This may have been resolved previously but I cannot find the answer so if anyone can help, I'd appreciate it.

 

I have 5 pages of equations that use variables stated at the very top. I want to have a table at the end stating that if a single variable changes at the beginning, this is how the final equations calculate out. Is there a way to do this? Thanks in advance.

9 REPLIES 9

Re: Solving equations with changing 1 variable


@eberg770 wrote:

 

I have 5 pages of equations that use variables stated at the very top. I want to have a table at the end stating that if a single variable changes at the beginning, this is how the final equations calculate out. Is there a way to do this? Thanks in advance.



Well. . . sort of.   Mathcad isn't really big on tables.

 

See the attachment (in Mathcad 15 so you might have to convert if you're a Prime user.)  Note that you must recopy the "results" computation after changing the variable value.

Re: Solving equations with changing 1 variable

do you mean more precisely that constants are defined at the top? and if one of them varies, all results will automatically change. This is normal. It happens the same that if a variable has assumed a constant value, the functions will give constant values and will take on another value if the variable assumes another constant value.

Re: Solving equations with changing 1 variable

Its a long standing wish that we'd like to be able to turn a worksheet into a function but until now no development steps were made in this direction.

All you can do is to turn all your equations into functions depend on the variable you'd like to change. So at the end end you could call the final function  with a set (vector) of different input values.

I am aware that rewriting the 5-page calculation can be quite cumbersome and may also destroy the clearness/readability of the calculation.

Here is a very simple example of what I am talking about.

Instead of making the calculation straightforward

B1.PNG

you turn them into functions of the changeable input variable a and create a table at the end:

B2.PNG

Making the calculation depended on more than one input works the same way:

B3.PNG

Re: Solving equations with changing 1 variable

What you want is normal operation of Mathcad. Or I don't understand your question.

 

Mathcad works top to bottom, left to right.

Any variable that is defined top/left of its use (in an operation or function) is used per its defined value, and when the definition changes the result is reflected in the use (result of operation or function).

At the end of the worksheet you can evaluate all your inputs and outputs, put them side by side if you wish, or assemble them into an array or matrix (Table?). Whatever you like.

This all: PROVIDED you have automatic calculation switched on.... If not, you must recalculate the sheet to see the results of changing a variable (in Mathcad , press F9).

 

If you're using Prime and want to use its 'Table' feature to present the results at the end of the worksheet, than you may have bad luck. See here: https://community.ptc.com/t5/PTC-Mathcad-Questions/Operaciones-dentro-de-tabla/m-p/553019#M180884

 

Success!
Luc

Re: Solving equations with changing 1 variable

Thank you for your responses. They have helped however I may have been a bit too vague in my original posted question. Let me explain with a little more detail...

 

I am designing a beam and need to determine the capacity of the beam in compression and bending. However, the beam has multiple points for the unbraced length to be assigned. I want to have it where the document shows the maximum unbraced length (worst case scenario with value assigned) calculations through and then as the end, show a "table" of what the capacity could be if the unbraced length were shortened to various distances. I can do this by hand by changing my length dimension on top and it would auto-calculate and I can create my own excel table to have on my document however I was hoping there was a way that mathcad could do it for me.

 

Thanks again for your help.

Re: Solving equations with changing 1 variable

You can still do that, if you put your calculation for capacity in a function with unbraced length as a parameter. Then you can have mathcad find the unbraced length that goes with e.g. the maximum, or any desired capacity. And the function will also allow you to calculate a table of capacity values for any list of unbraced length values.

 

Success!
Luc

Re: Solving equations with changing 1 variable


@eberg770 wrote:

Thank you for your responses. They have helped however I may have been a bit too vague in my original posted question. Let me explain with a little more detail...

 

I am designing a beam and need to determine the capacity of the beam in compression and bending. However, the beam has multiple points for the unbraced length to be assigned. I want to have it where the document shows the maximum unbraced length (worst case scenario with value assigned) calculations through and then as the end, show a "table" of what the capacity could be if the unbraced length were shortened to various distances. I can do this by hand by changing my length dimension on top and it would auto-calculate and I can create my own excel table to have on my document however I was hoping there was a way that mathcad could do it for me.

 

Thanks again for your help.


So it looks that I had interpreted your question correctly.

As I already said there is no convenient way to do it. You will have to turn all calculations into functions which depend on the input variable you want to change.

My very simple example above should show how this must be done.

Re: Solving equations with changing 1 variable

Hi,

 

Would a graph do instead of a table.  Moment and Compression capacity versus effective length.

 

You will need to adjust the reference and input file names depending on where you place the files in the zip.

 

To design simply calculate the effective length look at a graph too choose the size..

 

Cheers Terry

Re: Solving equations with changing 1 variable

We can do that, but not well:

Capture.PNGsee attached