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Liv7-Bedrock
7-Bedrock
September 19, 2016
Solved

Sum of series. Symbolic vs numeric

  • September 19, 2016
  • 2 replies
  • 10807 views

Why I'm getting different results for the sum in the attached worksheet with the symbolic and numeric evaluations ?

I think I've made somewhere a mistake..., but I cannot find where.

Probably I am so far not able to see the forest behind the tree...

Many thanks for help, Liv.

The worksheet was saved in Mcd11, but same results in Mcd15.

Best answer by AlvaroDíaz

Hi Richard.

Yes, it's not enough to make this difference.

Then the discrepancy is this other: using symbolic it's assumed that in a summative, the upper limit is biggest than the lower limit, but not in the numerical evaluation. The difference between both values (1/12) came from this, as it's showed in the attached. Also is the cause of the discrepancy identified by Fred.

Best regards.

Alvaro.

round.gif

2 replies

A
AlvaroDíaz12-Amethyst
12-Amethyst
September 19, 2016

Hi Liviu.

It's just a round error. For example, if you modify the expression for the sumatorie, get a better numerical result, as is showed in the attached.

Best regards.

Alvaro.

round.gif

R
RichardJ19-Tanzanite
19-Tanzanite
September 19, 2016

I'm not sure you are right. I don't believe this should have any significant numerical error:

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
September 19, 2016

The individual elements calculate correctly:

But the summations don't correlate:

L
Liv7-BedrockAuthor
7-Bedrock
September 19, 2016

Thank you a lot for considering my issue and for the prompt answers.

I've started to write my problem in Mathcad in more detail, pretty much like Fred did above, but not finished since left for work.

After posting I've noticed too that there is a term in the beginning of the series with an upper limit of summation smaller than the lower limit and that might generate inconsistency or/and the error in numeric evaluation.

Best, Liv.

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