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INTEGRAL (TRAPEZOIDAL RULE)


## This m-file computes the integral of a function f over the
## equally spaced points x using the trapezoidal rule.
function I = trapezoid(x,f)
h = x(2)-x(1);
N = length(f);
I = 0;
for n=2:N-1,
I = I + h*f(n);
endfor
I = I + h/2*(f(1) + f(N));
endfunction

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NEWTON-RAPSON METHOD-8th degree Legendre polynomial

## Newton-Rapson Method to the smallest non negative root
## of the 8th degree Legendre Polynomial
## P8(x)=(1/128)(6435x^8-12012x^6+6930x^4-1260x^2+35)
## where -1<=x<=1.
## for the smallest non negative root, we can ignore
## all the terms except the last two by truncated
## the function to be zero and find
## x=0.167 as the initial smallest non negative
## root.
##Constants and initializations
x=[]; ## Empty array for the iterated x roots
x(1)=0.16700000; ## Initial guess to begin the iteration for the
## smallest non-negative root.
L8=[]; ## Empty array for the Legendre polynomial
L8p=[]; ## Empty array for the derivative of the Legendre polynomial
for i=1:100
##The value of the function at x
L8(i)=(1/128)*(6435*x(i)^8-12012*x(i)^6+6930*x(i)^4-1260*x(i)^2+35);
##The value of the derivative of the function at x
L8p(i)=(1/128)*(6435*8*x(i)^7-12012*6*x(i)^5+6930*4*x(i)^3-1260*2*x(i));
x(i+1)=x(i)-L8(i)/L8p(i); ## the iteration
endfor
## For plot let's define a new variable…

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gnuplot> set xrange [-180:180] gnuplot> set yrange [-180:180] gnuplot> set pm3d gnuplot> set hidden3d  gnuplot> set title 'SHG' gnuplot> splot sin(cos(x*pi/180))*sin(cos(x*pi/180))/(cos(x*pi/180)*cos(x*pi/180))*sin(cos(y*pi/180))*sin(cos(y*pi/180))/(cos(y*pi/180)*cos(y*pi/180)) title 'N=1
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