Mathematica

Stop mathematica reordering expression during matrix
Hi Robert, One way to do what you want would be to disable the Orderless attribute of Times temporarily during the evaluation of your code: In[54]:= Unprotect[Times]; ClearAttributes[Times,Orderless]; C2=C1.C1; result = Hold[Evaluate[C2]]; SetAttributes[Times,Orderless]; Protect[Times]; In[60]:= resul... 25 Apr 2010 06:35

Kernel crash, version 7.0, windows XP, when using
I have version 7.0.1 on a Mac $Version 7.0 for Mac OS X x86 (64-bit) (February 19, 2009) I do not get this behavior. Do you get the same problem by changing the control label (small number in the gray area just to the right of the control)? Bob Hanlon ---- "Nasser M. Abbasi" <nma(a)12000.org> wrote: ... 25 Apr 2010 06:35

How to make GraphicsGrid use different cell sizes?
Version 7: I never used GraphicsGrid before, and could not find a way to adjust the size of each "cell" to remove the empty space around each entry in the GraphicsGrid. Here is a screen shot to help explain my question: http://12000.org/tmp/graphics_grid_mathematica/q.PNG For example, if you run this co... 25 Apr 2010 06:35

EquationTrekker for system of two 1st order ODEs
Is it possible to use the EquationTrekker package to plot solutions of a system of two first-order ODEs? With Mathematica 7.0.1, I try: <<EquationTrekker` EquationTrekker[ {x'[t] == 2 x[t] + 3 y[t], y'[t] == x[t] - y[t]}, {x, y}, {t, 0, 20}, PlotRange -> {{-5, 5}, {-5, 5}}] Up ... 24 Apr 2010 05:01

Function to detect presence of a variable in expression
I would like to have a function k = CountMeIn[expr,var] that returns the number of times var appears in expr, eg. CountMeIn[(1/x)^x,x] returns 2. var could be a list, in which case k would be a conforming list: k = CountMeIn[(2/x)^(x*w^4*z),{x,y,w,z}] should return {2,0,1,1}. expr is never a list... 24 Apr 2010 05:01

LeastSquares vs. Pseudoinverse
Hello Group, What is the difference of those when solving the problem A.x=b? What are the difference scenarios of one vs. the other? best regards, Eric ... 25 Apr 2010 06:35

Kernel crash using Z transform, version 7, windows
I get the same crash; however, if I both Rationalize AND Simplify (but NOT FullSimplify) first, then $Version 7.0 for Mac OS X x86 (64-bit) (February 19, 2009) expr = 0.20056791381984598*I* E^((-2.3120000000000003 - 2.4929211780559766*I)*n) - 0.20056791381984598*I* E^((-2.312000000000... 23 Apr 2010 20:53

Kernel crash using Z transform, version 7, windows XP, SP2.
Warning, do not run this before saving your work: In[1]:= ClearAll["Global`*"]; expr = 0.20056791381984598*I*E^((-2.3120000000000003 - 2.4929211780559766*I)*n) - 0.20056791381984598*I*E^((-2.3120000000000003 + 2.4929211780559766*I)*n); ZTransform[expr, n, z, Method -> "Holonomic"] *kernel crash* Bu... 23 Apr 2010 20:53

formula indexing
Considering the way that mathematica simplifes, can anyone reference some kind of cool that is like a search engine that can parse algebraic structures and identified them regardless of what the variables used? ... 23 Apr 2010 20:53

Solving Non-linear Differential Equations using DSolve
Hello! I'm having a problem solving non linear ordinary differential equations: when I try to solve this system, I get this error "Equations may not give solutions for all "solve" variables." The system is this: DSolve[{X8'[t] == C1 - C2 - k1*X1[t]*X8[t], X8[t1] == X8t1, X2'[t] == (-k2)*X2[t] + k1*X1[t]*X8[t... 23 Apr 2010 20:53