Subject: tips for Multiple roots of non-algebric equations
From: Raymond Toy
Date: Mon, 05 Jan 2009 10:51:12 -0500
>>>>> "Luigi" == Luigi Marino <luigi_marino2 at alice.it> writes:
Luigi> I try to solve non-algebric equations with multiple roots. :
Luigi> 1. first example.
Luigi> f:log(x^2+1)-sin(x)-4;
Luigi> for k:-12 thru -3 step 1 do print("x="(newton(f,x,k,0.0000000001)))$
Luigi> x=(-11.473978752837)
Luigi> x=(-11.47397875283699)
Are you bothered that you get the same roots again?
Luigi> 3. third example
Luigi> h:log(x+1)-1/2*x^2+0.6;(%o13)
Luigi> log(x+1)-x^2/2+0.6(%i14)
Luigi> for k:0 thru 1 step 1 do print("x="(newton(h,x,k,0.0000000001)))$
Luigi> x=(-0.40442128319509)
Luigi> x=(1.806649648414053)
Are you bothered that you get roots outside of the interval [0,1]?
I think that's the nature of Newton's method. Your initial guess has
to be close enough to the root to converge to the root; different
starting points can converge to the same root. And nothing constrains
Newton's method to stay in any given interval.
Ray