Gauss Legendre numerical intergration

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Discussion Overview

The discussion revolves around Gauss Legendre numerical integration, specifically focusing on the substitution process in a solved example and the disappearance of certain coefficients in the calculations. Participants seek clarification on the mathematical steps involved, particularly regarding the values of coefficients and roots used in the integration process.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant expresses confusion about the substitution process in the solved example and questions why a2=2 seems to disappear in the final answer.
  • Another participant asserts that for n=2, a2=1, but questions the absence of a1=2 in the calculations.
  • A participant provides a detailed breakdown of the integration formula used for n=2, including specific values for r1 and r2, and explains that only the values for n=2 are relevant in the calculations.
  • The calculations presented include specific numerical values and exponential functions, leading to a final computed result of approximately 1.5617973919398203851893261344599.
  • It is noted that the values of α and r for other n are not used in this case, and that the handout implied the use of ones for certain coefficients.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasoning behind the disappearance of certain coefficients, and multiple viewpoints regarding the values of a1 and a2 are presented. The discussion remains unresolved regarding the clarity of the substitution process.

Contextual Notes

There are limitations in the clarity of the mathematical steps presented, particularly regarding the assumptions made about the coefficients and their implications in the integration process.

Sadeq
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Gauss Legendre numerical intergration
The attachment file contain solved example
i don't know how he subsitute and why a2=2 done disappear in the answer
please expalin in details
 

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n=2
so
a2=1
 
lurflurf said:
n=2
so
a2=1

What about a1=2
doent apper
could u explain more pls
 
sure, we have from the handout and Gauss Legendre numerical integration
I=α1α1r12e^r1
1α2r12e^r2
2α1r22e^r1
2α2r22e^r2
now since n=2 we use
r1=-1/sqrt(3)~-0.57735026918962576450914878050196
r2=1/sqrt(3)~0.57735026918962576450914878050196
α1=1~1.000000000000000000000000000000000
αsub]2[/sub]=1~1.000000000000000000000000000000000

So just substitute in the values to find I
I=(4/3)cosh(1/sqrt(3))
=(1.000000000000000000000000000000000)(1.000000000000000000000000000000000)(-0.57735026918962576450914878050196)2e^-0.57735026918962576450914878050196
+(1.000000000000000000000000000000000)(1.000000000000000000000000000000000)(-0.57735026918962576450914878050196)2e^0.57735026918962576450914878050196
+(1.000000000000000000000000000000000)(1.000000000000000000000000000000000)(0.57735026918962576450914878050196)2e^-0.57735026918962576450914878050196
+(1.000000000000000000000000000000000)(1.000000000000000000000000000000000)(0.57735026918962576450914878050196)2e^0.57735026918962576450914878050196
=1.5617973919398203851893261344599

notice that only the values of α and r for n=2 are used
The values of α and r for other n are not used
In the handout all the ones were implied
 
Last edited:
thank you brother
 

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