Difference in results between excel and Mathcad

[dipeshchauhan]

Hi ,

I have a Implicit equation to solve , but with the same set of the parameter value i am finding two different curve.

The way i am trying ,

• Use Excel to iterate by resolving it's circular reference
  
• Using Mathcad solver block (Given and find)
  

Please help me in that.

[dipeshchauhan]

Mathcad 11 ver. file attached

[AlanStevens]

Your Mathcad formula was wrong - be very careful where you put your brackets!!

Alan

[RichardJ]

Your Mathcad formula was wrong - be very careful where you put your brackets!!

The Mathcad one or the Eccel one? I found the same thing, but assumed that the one in Excel was probably wrong.

[AlanStevens]

I think it's the Mathcad one that is wrong as the value of I at V=Voc should be zero. Also, there were differences in the values of Rp and ekt used between the Mathcad and Excel worksheets, though I think the misplaced brackets provided the major source of error.

Alan

[RichardJ]

I think it's the Mathcad one that is wrong as the value of I at V=Voc should be zero.

OK. I don't even know what Voc is, and based my assumption on the fact that it's orders of magnitude easier to screw up a formula in Excel than it is in Mathcad.

Also, there were differences in the values of Rp and ekt used between the Mathcad and Excel worksheets, though I think the misplaced brackets provided the major source of error.

Yes, I also saw those, but changing them makes little difference. As you say, it's the brackets that are the real problem.

[AlanStevens]

Richard Jackson wrote:

OK. I don't even know what Voc is, and based my assumption on the fact that it's orders of magnitude easier to screw up a formula in Excel than it is in Mathcad.

Nor do I, but in an earlier post with the same system Dipesh mentioned that I should be zero when V=Voc.

I totally agree with your comment about Excel - in fact, the equation written in cell C5 of the Excel spreadsheet is dfifferent from the ones actually used in the calculations (there's an unmatched bracket). I suspect that the Excel spreadsheet was developed first and then the formula (mis)copied into Mathcad.

Alan

[RichardJ]

I totally agree with your comment about Excel - in fact, the equation written in cell C5 of the Excel spreadsheet is dfifferent from the ones actually used in the calculations (there's an unmatched bracket).

We seem to have gone through almost exactly the same exercise! I've deleted everything now so I can't check, but I think there are actually three unmatched brackets.

[LouP]

Assuming that Voc has its usual elect. eng. meaning - open circuit voltage - then by definition the current should be zero at this value, so it is a reasonable assumption. I didn't check this in the mathcad sheet, so its formula may well be wrong. I agrre that the Excel syntax has errors, but I don't know what's correct. One thing I did check, and that I recommend to anyone (Dipesh : - ) solving any complex nonlinear equation is to check the solution. Whether the matchad equation is wrong or not, the solution found does satisfy the equation. I set up a fct. to eval the right side of the equation as a fct. of V and I, then checked to see if this gave the value I on left side. It did. Worth checking if solved in Excel, too.

Lou

[RichardJ]

Assuming that Voc has its usual elect. eng. meaning - open circuit voltage

Thanks for the clarification

[dipeshchauhan]

Thanks Allan , My problem is solved now. It is "bracket" problem .

I should have notice it, but any way thanks .

[MikeArmstrong]

DONT USE EXCEL !!!!!!!!!

Mike