Hi, I just installed Octave and thought I would give it a try. I tried to solve a trivial equation: 8 = 2 * x + 4 what is x? When I type the equation, Octave complains that x is undefined. The only way I can get Octave to solve for x is to do half the work myself by transforming the equation, such that x is alone on the left side of the equation: x = (8 - 4) / 2 Only then does Octave reply that: x = 2 How do I give Octave an equation or a set of equations and then ask it to solve them? A slightly less trivial example is: 10 = x * y + 2 8 = 2 * y + x what are x and y? In this case, I could not transform the equations as above because the transformation of the first equation to x = ... is not resolvable without the second equation, so it would complain that y is undefined. And if I transformed it to y = ..., it would complain that x is undefined. In this case, (before the second equation is defined) x and y are unknowable. So what syntax do I use to submit both equations simultaneously to Octave, so that it can solve these simultaneously? Of course, I could transform the equations and use substitution, but again I would be doing half the work by hand. I have scanned through the help documentation, but such simple issues are not addressed. Can anyone give me a few examples of syntax I would submit to address these trivial equations? Thanks, Joe _______________________________________________ Help-octave mailing list [hidden email] https://www-old.cae.wisc.edu/mailman/listinfo/help-octave |
On Tue, May 19, 2009 at 4:45 PM, Joe Kirchner <[hidden email]> wrote:
> Hi, > > I just installed Octave and thought I would give it a try. > > I tried to solve a trivial equation: > > 8 = 2 * x + 4 > > what is x? > > When I type the equation, Octave complains that x is undefined. The only > way I can get Octave to solve for x is to do half the work myself by > transforming the equation, such that x is alone on the left side of the > equation: > > x = (8 - 4) / 2 > > Only then does Octave reply that: > > x = 2 > > How do I give Octave an equation or a set of equations and then ask it to > solve them? > > A slightly less trivial example is: > > 10 = x * y + 2 > 8 = 2 * y + x > > what are x and y? > > In this case, I could not transform the equations as above because the > transformation of the first equation to x = ... is not resolvable without > the second equation, so it would complain that y is undefined. And if I > transformed it to y = ..., it would complain that x is undefined. In this > case, (before the second equation is defined) x and y are unknowable. So > what syntax do I use to submit both equations simultaneously to Octave, so > that it can solve these simultaneously? > > Of course, I could transform the equations and use substitution, but again I > would be doing half the work by hand. > > I have scanned through the help documentation, but such simple issues are > not addressed. > > Can anyone give me a few examples of syntax I would submit to address these > trivial equations? > > Thanks, > > Joe > Octave is not a CAS, which is what you apparently want, but rather a numerical tool. It can solve equations (linear, nonlinear) only approximately, and needs them specified in some canonical form. For more info, see: http://en.wikipedia.org/wiki/Computer_algebra_system regards -- RNDr. Jaroslav Hajek computing expert & GNU Octave developer Aeronautical Research and Test Institute (VZLU) Prague, Czech Republic url: www.highegg.matfyz.cz _______________________________________________ Help-octave mailing list [hidden email] https://www-old.cae.wisc.edu/mailman/listinfo/help-octave |
In reply to this post by Joe_K
On Tue, May 19, 2009 at 4:45 PM, Joe Kirchner <[hidden email]> wrote:
> Hi, > > I just installed Octave and thought I would give it a try. > > I tried to solve a trivial equation: > > 8 = 2 * x + 4 > > what is x? > > When I type the equation, Octave complains that x is undefined. The only > way I can get Octave to solve for x is to do half the work myself by > transforming the equation, such that x is alone on the left side of the > equation: > > x = (8 - 4) / 2 > > Only then does Octave reply that: > > x = 2 > > How do I give Octave an equation or a set of equations and then ask it to > solve them? > > A slightly less trivial example is: > > 10 = x * y + 2 > 8 = 2 * y + x > > what are x and y? > > In this case, I could not transform the equations as above because the > transformation of the first equation to x = ... is not resolvable without > the second equation, so it would complain that y is undefined. And if I > transformed it to y = ..., it would complain that x is undefined. In this > case, (before the second equation is defined) x and y are unknowable. So > what syntax do I use to submit both equations simultaneously to Octave, so > that it can solve these simultaneously? > > Of course, I could transform the equations and use substitution, but again I > would be doing half the work by hand. > > I have scanned through the help documentation, but such simple issues are > not addressed. > > Can anyone give me a few examples of syntax I would submit to address these > trivial equations? > > Thanks, > > Joe Hi Octave is a programming language, so it can't "magically" solve any equation you enter. In fact, "=" is used for assignment, not equality, so your example "8 = 2 * x + 4" is interpreted as "compute 2*x+4 and assign it to 8", which does not make sense (since x is undefined and 8 is a constant). On the other hand, "x = (8 - 4) / 2" is valid since right side is a mathematical expression that is evaluated to a number, which is then assigned to variable x. I hope this made some sense, I suggest you take look at chapter 1 of Octave manual ("A Brief Introduction to Octave") which gives some simple examples. To solve set of linear equations Ax = b (written in matrix form), you must specify matrix A, vector b and then solve by "x = A\b". For nonlinear equations, you must use "fsolve" function. Regards Ivan Sutoris _______________________________________________ Help-octave mailing list [hidden email] https://www-old.cae.wisc.edu/mailman/listinfo/help-octave |
In reply to this post by Joe_K
>I tried to solve a trivial equation:
> >8 = 2 * x + 4 > >what is x? You want symbolic equation solving. Octave is not made for it, event though it has an optional symbolic package that can do some symbolic computations. However this makes sense only if you use Octave for what it does best, that is numeric computations, and you need the occasional symbolic computation. For a symbolic package, you could try Maxima. -- Francesco Potortì (ricercatore) Voice: +39 050 315 3058 (op.2111) ISTI - Area della ricerca CNR Fax: +39 050 315 2040 via G. Moruzzi 1, I-56124 Pisa Email: [hidden email] (entrance 20, 1st floor, room C71) Web: http://fly.isti.cnr.it/ _______________________________________________ Help-octave mailing list [hidden email] https://www-old.cae.wisc.edu/mailman/listinfo/help-octave |
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