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In the late 1970s it was noted that by evaluating PowerMod[a, n - 1, n] 1 for several random integers a one can with high probability quickly deduce PrimeQ[n] .
Here are examples of how some of the basic Mathematica constructs used in the notes in this book work:
• Iteration
Nest[f, x, 3] ⟶ f[f[f[x]]]
NestList[f, x, 3] ⟶ {x, f[x], f[f[x]], f[f[f[x]]]}
Fold[f, x, {1, 2}] ⟶ f[f[x, 1], 2]
FoldList[f, x, {1, 2}] ⟶ {x, f[x, 1], f[f[x, 1], 2]}
• Functional operations
Function[x, x + k][a] ⟶ a + k
(# + k&)[a] ⟶ a + k
(r[#1] + s[#2]&)[a, b] ⟶ r[a] + s[b]
Map[f, {a, b, c}] ⟶ {f[a], f[b], f[c]}
Apply[f, {a, b, c}] ⟶ f[a, b, c]
Select[{1, 2, 3, 4, 5}, EvenQ] ⟶ {2, 4}
MapIndexed[f, {a, b, c}] ⟶ {f[a, {1}], f[b, {2}], f[c, {3}]}
• List manipulation
{a, b, c, d} 〚 3 〛 ⟶ c
{a, b, c, d} 〚 {2, 4, 3, 2} 〛 ⟶ {b, d, c, b}
Take[{a, b, c, d, e}, 2] ⟶ {a, b}
Drop[{a, b, c, d, e}, -2] ⟶ {a, b, c}
Rest[{a, b, c, d}] ⟶ {b, c, d}
ReplacePart[{a, b, c, d}, x, 3] ⟶ {a, b, x, d}
Length[{a, b, c}] ⟶ 3
Range[5] ⟶ {1, 2, 3, 4, 5}
Table[f[i], {i, 4}] ⟶ {f[1], f[2], f[3], f[4]}
Table[f[i, j], {i, 2}, {j, 3}] ⟶ {{f[1, 1], f[1, 2], f[1, 3]}, {f[2, 1], f[2, 2], f[2, 3]}}
Array[f, {2, 2}] ⟶ {{f[1, 1], f[1, 2]}, {f[2, 1], f[2, 2]}}
Flatten[{{a, b}, {c}, {d, e}}] ⟶ {a, b, c, d, e}
Flatten[{{a, {b, c}}, {{d}, e}}, 1] ⟶ {a, {b, c}, {d}, e}
Partition[{a, b, c, d}, 2, 1] ⟶ {{a, b}, {b, c}, {c, d}}
Split[{a, a, a, b, b, a, a}] ⟶ {{a, a, a}, {b, b}, {a, a}}
ListConvolve[{a, b}, {1, 2, 3, 4, 5}] ⟶ {2a + b, 3a + 2b, 4a + 3b, 5a + 4b}
Position[{a, b, c, a, a}, a] ⟶ {{1}, {4}, {5}}
RotateLeft[{a, b, c, d, e}, 2] ⟶ {c, d, e, a, b}
Join[{a, b, c}, {d, b}] ⟶ {a, b, c, d, b}
Union[{a, a, c, b, b}] ⟶ {a, b, c}
• Transformation rules
{a, b, c, d} /. b p ⟶ {a, p, c, d}
{f[a], f[b], f[c]} /. f[a] p ⟶ {p, f[b], f[c]}
{f[a], f[b], f[c]} /. f[x_] p[x] ⟶ {p[a], p[b], p[c]}
{f[1], f[b], f[2]} /. f[x_Integer] p[x] ⟶ {p[1], f[b], p[2]}
{f[1, 2], f[3], f[4, 5]} /. f[x_, y_] x + y ⟶ {3, f[3], 9}
{f[1], g[2], f[2], g[3]} /. f[1] | g[_] p ⟶ {p, p, f[2], p}
• Numerical functions
Quotient[207, 10] ⟶ 20
Mod[207, 10] ⟶ 7
Floor[1.45] ⟶ 1
Ceiling[1.45] ⟶ 2
IntegerDigits[13, 2] ⟶ {1, 1, 0, 1}
IntegerDigits[13, 2, 6] ⟶ {0, 0, 1, 1, 0, 1}
DigitCount[13, 2, 1] ⟶ 3
FromDigits[{1, 1, 0, 1}, 2] ⟶ 13
The Mathematica programs in these notes are formatted in Mathematica StandardForm .
One marginally more complicated case effectively involving 13 neighbors is
IsingEvolve[list_, t_Integer] := First[Nest[IsingStep, {list, Mask[list]}, t]]
IsingStep[{a_, mask_}] := {MapThread[ If[#2 2 && #3 1, 1 - #1, #1]&, {a, ListConvolve[ {{0, 1, 0}, {1, 0, 1}, {0, 1, 0}}, a, 2], mask}, 2], 1 - mask}
where
Mask[list_] := Array[Mod[#1 + #2, 2]&, Dimensions[list]]
is set up so that alternating checkerboards of cells are updated on successive steps.
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