solve
in [Matlab]
|
From: Ben on 14 Jul 2010 09:11 Hello, I don't know how to use the solve function. I've read the matlab doc, but I don't know how to solve this problem. I have the following parameters. a =-1; b = 1.5; c = 0; I want to use this equation: A = solve('a*cos(x) - b*sin(x)=c'); This gives: A = (-2)*atan((b - (a^2 + b^2 - c^2)^(1/2))/(a + c)) (-2)*atan((b + (a^2 + b^2 - c^2)^(1/2))/(a + c)) How can I get the answer in numbers between -pi and pi?
From: Steven Lord on 14 Jul 2010 13:22 "Ben" <benvoeveren(a)gmail.com> wrote in message news:279599969.28875.1279127546346.JavaMail.root(a)gallium.mathforum.org... > Hello, > > I don't know how to use the solve function. I've read the matlab doc, but > I don't know how to solve this problem. > > I have the following parameters. > > a =-1; > b = 1.5; > c = 0; > > I want to use this equation: > A = solve('a*cos(x) - b*sin(x)=c'); > > This gives: > A = > (-2)*atan((b - (a^2 + b^2 - c^2)^(1/2))/(a + c)) > (-2)*atan((b + (a^2 + b^2 - c^2)^(1/2))/(a + c)) > > How can I get the answer in numbers between -pi and pi? Use SUBS to substitute values into the expression. -- Steve Lord slord(a)mathworks.com comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ To contact Technical Support use the Contact Us link on http://www.mathworks.com
From: Roger Stafford on 14 Jul 2010 21:13 Ben <benvoeveren(a)gmail.com> wrote in message <279599969.28875.1279127546346.JavaMail.root(a)gallium.mathforum.org>... > Hello, > > I don't know how to use the solve function. I've read the matlab doc, but I don't know how to solve this problem. > > I have the following parameters. > > a =-1; > b = 1.5; > c = 0; > > I want to use this equation: > A = solve('a*cos(x) - b*sin(x)=c'); > > This gives: > A = > (-2)*atan((b - (a^2 + b^2 - c^2)^(1/2))/(a + c)) > (-2)*atan((b + (a^2 + b^2 - c^2)^(1/2))/(a + c)) > > How can I get the answer in numbers between -pi and pi? - - - - - - - - My symbolic toolbox came up with the same answer, Ben . However, this form of expression can produce a NaN where none ought to occur. For example, let a = 1, b = 1, and c = -1, which is a perfectly reasonable combination of values. However, the first of the two symbolic expressions when computed numerically with double precision numbers will give rise to a NaN because it involves a zero-divided-by-zero situation. This is an entirely artificial difficulty; there ought to be no trouble with that combination of values for a, b, and c. I much prefer the following two expressions: A = [mod(atan2(b,-a)+acos(c/sqrt(a^2+b^2)),2*pi)-pi; mod(atan2(b,-a)-acos(c/sqrt(a^2+b^2)),2*pi)-pi] These values will also always fall between -pi and +pi. The only accuracy difficulty this encounters occurs when c/sqrt(a^2+b^2) is very nearly +1 or -1, and that is inherent in the problem. A tiny change in c here makes a much larger change in x. The symbolic expressions also have the same difficulty in that circumstance. Roger Stafford
|
Pages: 1 Prev: fzero probably easy fix Next: Matrix Rotation About Origin |