symbolic maths
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From: Mario Fatafehi on 28 Mar 2010 23:37 how can i solve the 5*x^3 +10*x^2-7*x+1=0.I can't find any example similar to this problem. Any help?
From: us on 29 Mar 2010 01:09 "Mario Fatafehi" <coruba9(a)hotmail.com> wrote in message <hop790$nm$1(a)fred.mathworks.com>... > how can i solve the 5*x^3 +10*x^2-7*x+1=0.I can't find any example similar to this problem. Any help? a hint: help sym; help solve; us
From: Mario Fatafehi on 29 Mar 2010 02:34 "us " <us(a)neurol.unizh.ch> wrote in message <hopclf$lo7$1(a)fred.mathworks.com>... > "Mario Fatafehi" <coruba9(a)hotmail.com> wrote in message <hop790$nm$1(a)fred.mathworks.com>... > > how can i solve the 5*x^3 +10*x^2-7*x+1=0.I can't find any example similar to this problem. Any help? > > a hint: > > help sym; > help solve; > > us [x]=solve('5*x^3 +10*x^2-7*x+1=0') gives me very strange result. help? x = 1/30*(-23300+60*i*2355^(1/2))^(1/3)+82/3/(-23300+60*i*2355^(1/2))^(1/3)-2/3 -1/60*(-23300+60*i*2355^(1/2))^(1/3)-41/3/(-23300+60*i*2355^(1/2))^(1/3)-2/3+1/2*i*3^(1/2)*(1/30*(-23300+60*i*2355^(1/2))^(1/3)-82/3/(-23300+60*i*2355^(1/2))^(1/3)) -1/60*(-23300+60*i*2355^(1/2))^(1/3)-41/3/(-23300+60*i*2355^(1/2))^(1/3)-2/3-1/2*i*3^(1/2)*(1/30*(-23300+60*i*2355^(1/2))^(1/3)-82/3/(-23300+60*i*2355^(1/2))^(1/3))
From: us on 29 Mar 2010 02:43 "Mario Fatafehi" <coruba9(a)hotmail.com> wrote in message <hophkt$497$1(a)fred.mathworks.com>... > "us " <us(a)neurol.unizh.ch> wrote in message <hopclf$lo7$1(a)fred.mathworks.com>... > > "Mario Fatafehi" <coruba9(a)hotmail.com> wrote in message <hop790$nm$1(a)fred.mathworks.com>... > > > how can i solve the 5*x^3 +10*x^2-7*x+1=0.I can't find any example similar to this problem. Any help? > > > > a hint: > > > > help sym; > > help solve; > > > > us > > [x]=solve('5*x^3 +10*x^2-7*x+1=0') gives me very strange result. help? > > x = > > 1/30*(-23300+60*i*2355^(1/2))^(1/3)+82/3/(-23300+60*i*2355^(1/2))^(1/3)-2/3 > -1/60*(-23300+60*i*2355^(1/2))^(1/3)-41/3/(-23300+60*i*2355^(1/2))^(1/3)-2/3+1/2*i*3^(1/2)*(1/30*(-23300+60*i*2355^(1/2))^(1/3)-82/3/(-23300+60*i*2355^(1/2))^(1/3)) > -1/60*(-23300+60*i*2355^(1/2))^(1/3)-41/3/(-23300+60*i*2355^(1/2))^(1/3)-2/3-1/2*i*3^(1/2)*(1/30*(-23300+60*i*2355^(1/2))^(1/3)-82/3/(-23300+60*i*2355^(1/2))^(1/3)) well... the beauty of sym math... one of the solutions r=solve('5*x^3 +10*x^2-7*x+1=0'); r=double(r) %{ % r = 0.35553 +1.4013e-045i -2.5741 -7.0065e-046i 0.21854 -7.0065e-046i %} us
From: Steven Lord on 29 Mar 2010 09:49
"Mario Fatafehi" <coruba9(a)hotmail.com> wrote in message news:hop790$nm$1(a)fred.mathworks.com... > how can i solve the 5*x^3 +10*x^2-7*x+1=0.I can't find any example similar > to this problem. Any help? > For this particular example, there's no need to use symbolic computations. Just use ROOTS. P = [5 10 -7 1]; x = roots(P) polyval(P, x) If your expression were more complicated, but still a function of one variable, and numerically solving it was acceptable you could use FZERO. If you need a symbolic solution, use SOLVE as us has stated. -- Steve Lord slord(a)mathworks.com comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ |