Graph Forums — Error in area under graph

Re: Error in area under graph

null@example.com (agpallitit) — Fri, 07 May 2010 14:06:30 +0000

Thanks, the INF-possibility is just what I need to pass on to my pupils.

Re: Error in area under graph

null@example.com (Ivan Johansen) — Thu, 06 May 2010 21:42:37 +0000

In short it is a limitation of the algorithm used to calculate the area. Unfortunately there is no perfect algorithm for numeric integration, and Graph cannot do symbolic integration. If you look at the graph from -10000 to 0.8 it is actually very close to zero most of the way.

In the beta version of Graph 4.4, which I assume you are using, you can use -INF in the From field to indicate negative infinity. This usually give the best result for this kind of function instead of trying to find a negative number big enough.

Error in area under graph

null@example.com (agpallitit) — Thu, 06 May 2010 11:58:51 +0000

When I use the "Area under graph"-button to determine the area of e.g. dnorm(x,0.82,.08) from minus infinity to 0.8 i get the correct answer if i set the lower limit to -1000, and zero if i change the lower limit to -10000. Why is that?
(actually the change in value happens at a lower limit of -1410 i the example given above)