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I've been using Mathematica for awhile now and have never come even close to maxing out my CPU cycles. Are there any functions which consume lots of CPU cycles? Right now I am running a script which uses Parallelize and is consuming about 15%.

Also, a related question -- is there any way to get Mathematica to use more CPUs? It'd be nice to get to my answers faster.

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n = 100; While[True, MatrixPower[RandomReal[1, {#, #}], #] &[++n]] maxes my CPU out pretty quickly. –  Corey Kelly Jun 26 '13 at 18:25
n = 10000; A = RandomReal[1, {n, n}]; While[True, A.A]; –  Eric Brown Jun 26 '13 at 19:10
…but something tells me you are looking for saturation with a function that is called via the "Parallel" statement. –  Eric Brown Jun 26 '13 at 19:11
@EricBrown the highest load will almost certainly come from your suggestion of repeated multiplication of large matrices. Depending on how well the matrix-matrix multiply is optimized, the matrix size may need to be adjusted to fit into cache for optimum results. –  Oleksandr R. Jun 26 '13 at 19:22
@OleksandrR. Interesting you say that: on my Macbook Air (i7) the matrix multiply only uses two cores ("processors") whereas the Parallel operations, shown in my answer, get four (hyper threading?) –  Eric Brown Jun 26 '13 at 19:25
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1 Answer

up vote 2 down vote accepted

An example comes from the documentation:

localsol=Quiet@NDSolve[{D[u[t,x,y], t, t] == D[u[t,x,y], x,x] + D[u[t, x, y], y, y] + 
Sin[u[t,x,y]], u[t,-L, y] == u[t, L, y], u[t, x, -L] == u[t, x, L], 
u[0,x, y] == a Exp[-(b x^2 + y^2)], Derivative[1,0,0][u][0,x,y] == 0}, 
u, {t,0,L/2}, {x,-L,L},{y,-L,L}]; 

Plot3D[Evaluate[u[L/2, x, y] /. First[localsol]]
, {x,-L,L},{y,-L,L}
, PlotRange-> {{-L,L},{-L,L}, {-dz, dz}}
, {a, -0.5, 0.5, 0.2},{b,0.8,1.2,.1},Method->"FinestGrained"]

You can play with values of the step sizes of a and b, until you can fry an egg on your computer.

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Thanks for the script! This used ~50% of my 4 cores. I suppose that's because they are multi-threaded cores so I can have 8 threads going and Mathematica is using only 4 of them. –  lynvie Jun 26 '13 at 20:06
@lynvie my pleasure. Sounds reasonable, it's possible that it is cores instead of hyperthreading, but it is also possible that a) your license restricts you to 4 cores and/or b) you have the number of cores manually hard-wired in your Parallel Preferences. –  Eric Brown Jun 26 '13 at 20:12
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