• lhov
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Topic: Problem with integration / area under points

Hi

I've used Graph for  long time and I'm very pleased with the program.
But now it has occured a major problem when I plot the inverse of a function, the trapeze don't fit with the points!
Is there some settings I could change ?

Thanks in advance for your answer

Lars Harald Øvstetun

  • lhov
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Re: Problem with integration / area under points

For instance , I fix a point at (1/3,1/10) , the area between 0 and 1/3 should be 0.016666667 but instead I get 0.02666667, also the shaded area are above the fixed point.

Re: Problem with integration / area under points

I don't think I understand what it is you are doing. At least I am not able to reproduce it. Could you attach a .grf file that shows the problem?

  • lhov
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Re: Problem with integration / area under points

Hi, here's the graph-file.

I try to integrate these values.

The program does not figure out the right values, and also  the area under these points does not correspond visually either.

I've tried to reinstall the program, but is there any settings I could make?

  • lhov
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Re: Problem with integration / area under points

Here's the graph-file

Post's attachments

Attachment icon P invers plot.grf 814 b, 549 downloads since 2016-10-29 

Re: Problem with integration / area under points

I think you should sort the data points in increasing order of x-coordinates.

Post's attachments

area.png, 14.05 kb, 639 x 416
area.png 14.05 kb, 518 downloads since 2016-10-29 

  • lhov
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Re: Problem with integration / area under points

Oh,that I didn't think of, I thought I could do so!
Many thanks for your answer.

Lars Harald Øvstetun

Re: Problem with integration / area under points

Yes, as Benice says the points needs to be sorted for increasing x-values for this to work. The calculating of area under points is very simplistic implemented. Mostly because you enter from and to x-values. Therefore Graph cannot handle the line it is calculating the area under going through the same x-coordinate several times. It will always pick the first one. I think it becomes clear if you let Graph connect the points with a line.