Your first input prompt will be i1 : . In response to the prompt, type 2+2 and press return. The expression you entered will be evaluated - no punctuation is required at the end of the line.
The answer is displayed to the right of the output label
o1 =.
Here is some arithmetic with fractions.
i2 : 3/5 + 7/11
68
o2 = --
55
o2 : QQ
|
Notice the additional line of output labeled with o2 :. Output lines labeled with colons provide information about the type of output. In this case, the symbol QQ is our notation for the class of all rational numbers, and indicates that the answer on the previous line is a rational number.
Multiplication is indicated with
*.
Powers are obtained with
^.
i4 : 2^200
o4 = 1606938044258990275541962092341162602522202993782792835301376
|
Factorials are obtained with
!.
i5 : 40!
o5 = 815915283247897734345611269596115894272000000000
|
Because some answers can be very long, it is a good idea to run the program in a window that does not wrap output lines, and allows the user to scroll left horizontally to see the rest of the output. (See
using Macaulay2 with emacs.)
i6 : 100!
o6 = 933262154439441526816992388562667004907159682643816214685929638952175999
932299156089414639761565182862536979208272237582511852109168640000000000
00000000000000
|
Multiple expressions may be separated by semicolons.
A semicolon at the end of the line suppresses the printing of the value.
The output from the previous line can be obtained with
oo, even if a semicolon prevented it from being printed.
Lines before that can be obtained with
ooo and
oooo. Alternatively, the symbol labeling an output line can be used to retrieve the value, as in the following example.
i12 : o5 + 1
o12 = 815915283247897734345611269596115894272000000001
|
To enter a string, use quotation marks.
i13 : "hi there"
o13 = hi there
|
A value can be assigned to a variable with
=.
i14 : s = "hi there"
o14 = hi there
|
Strings may be concatenated horizontally with
|, (see
String | String).
i15 : s | " - " | s
o15 = hi there - hi there
|
or vertically with
||, (see
Net || Net).
i16 : s || " - " || s
o16 = hi there
-
hi there
|
A list of expressions can be formed with braces.
i17 : {1, 2, s}
o17 = {1, 2, hi there}
o17 : List
|
Lists behave like vectors.
i18 : 10*{1,2,3} + {1,1,1}
o18 = {11, 21, 31}
o18 : List
|
A function can be created with the arrow operator,
-> .
i19 : f = i -> i^3
o19 = f
o19 : FunctionClosure
|
To evaluate a function, place its argument to the right of the function.
Functions of more than one variable take a parenthesized sequence of arguments.
i21 : g = (x,y) -> x * y
o21 = g
o21 : FunctionClosure
|
i22 : g(6,9)
o22 = 54
|
The function
apply can be used to apply a function to each element of a list.
i23 : apply({1,2,3,4}, i -> i^2)
o23 = {1, 4, 9, 16}
o23 : List
|
i24 : apply({1,2,3,4}, f)
o24 = {1, 8, 27, 64}
o24 : List
|
The operator
.. may be used to generate sequences of consecutive numbers.
i25 : apply(1 .. 4, f)
o25 = (1, 8, 27, 64)
o25 : Sequence
|
If the first argument to
apply is an integer
n then it stands for the list
{0, 1, ..., n-1}.
i26 : apply(5, f)
o26 = {0, 1, 8, 27, 64}
o26 : List
|
The function
scan is analogous to
apply except that no value is returned. It may be used to implement loops in programs.
i27 : scan(5, i -> print (i, i^3))
(0, 0)
(1, 1)
(2, 8)
(3, 27)
(4, 64)
|
i28 : j=1; scan(10, i -> j = 2*j); j
o30 = 1024
|
Most computations with polynomials take place in rings that may be specified in usual mathematical notation.
(We reserve single letter symbols such as
Z for use as variables in rings, hence we must use something like
ZZ to stand for the ring of integers. It may remind you of the "blackboard bold" font of AMSTeX. If you prefer
Z to
ZZ, you may put
Z=ZZ in your
initialization file. The symbols
ZZ/5 represent the quotient ring
Z/5Z, and then
ZZ/5[x,y,z] represents the ring of polynomials in the variables x,y, and z with coefficients in the ring
Z/5Z.)
i32 : (x+y)^5
5 5
o32 = x + y
o32 : R
|
Rings and certain other types of things acquire the name of the global variable they are assigned to.
i33 : R
o33 = R
o33 : PolynomialRing
|
To see the original description of a ring, use
describe.
i34 : describe R
ZZ
o34 = --[x..z, Degrees => {3:1}, Heft => {1}]
5
|
A free module can be created as follows.
i35 : F = R^3
3
o35 = R
o35 : R-module, free
|
The i-th basis element of
F can be obtained as
F_i. In this example, the valid values for
i are 0, 1, and 2.
i36 : F_1
o36 = | 0 |
| 1 |
| 0 |
3
o36 : R
|
Using a list of indices instead will produce the homomorphism corresponding to the basis vectors indicated.
i37 : F_{1,2}
o37 = | 0 0 |
| 1 0 |
| 0 1 |
3 2
o37 : Matrix R <--- R
|
Repetitions are allowed.
i38 : F_{2,1,1}
o38 = | 0 0 0 |
| 0 1 1 |
| 1 0 0 |
3 3
o38 : Matrix R <--- R
|
We can create a homomorphism between free modules with
matrix by providing the list of rows of the matrix, each of which is in turn a list of ring elements.
i39 : f = matrix {{x,y,z}}
o39 = | x y z |
1 3
o39 : Matrix R <--- R
|
Use
image to get the image of f.
i40 : image f
o40 = image | x y z |
1
o40 : R-module, submodule of R
|
We may use
ideal to produce the corresponding ideal.
i41 : ideal (x,y,z)
o41 = ideal (x, y, z)
o41 : Ideal of R
|
We may use
kernel to compute the kernel of f.
i42 : kernel f
o42 = image {1} | -y 0 -z |
{1} | x -z 0 |
{1} | 0 y x |
3
o42 : R-module, submodule of R
|
The answer comes out as a module that is expressed as the image of a homomorphism whose matrix is displayed. Integers inside braces to the left of the matrix give the degrees of the basis elements of the target of the matrix; they are omitted if the degrees are all zero. In case the matrix itself is desired, it can be obtained with
generators, as follows.
i43 : generators oo
o43 = {1} | -y 0 -z |
{1} | x -z 0 |
{1} | 0 y x |
3 3
o43 : Matrix R <--- R
|
We may use
poincare to compute the Poincare polynomial.
i44 : poincare kernel f
2 3
o44 = 3T - T
o44 : ZZ[T]
|
We may use
rank to compute the rank.
i45 : rank kernel f
o45 = 2
|
A presentation for the kernel can be obtained with
presentation.
i46 : presentation kernel f
o46 = {2} | z |
{2} | x |
{2} | -y |
3 1
o46 : Matrix R <--- R
|
We can produce the cokernel with
cokernel; no computation is performed.
i47 : cokernel f
o47 = cokernel | x y z |
1
o47 : R-module, quotient of R
|
The direct sum is formed with
Module ++ Module.
i48 : N = kernel f ++ cokernel f
o48 = subquotient ({1} | -y 0 -z 0 |, {1} | 0 0 0 |)
{1} | x -z 0 0 | {1} | 0 0 0 |
{1} | 0 y x 0 | {1} | 0 0 0 |
{0} | 0 0 0 1 | {0} | x y z |
4
o48 : R-module, subquotient of R
|
The answer is expressed in terms of the
subquotient function, which produces subquotient modules. Each subquotient module is accompanied by its matrix of generators and its matrix of relations. These matrices can be recovered with
generators and
relations.
i49 : generators N
o49 = {1} | -y 0 -z 0 |
{1} | x -z 0 0 |
{1} | 0 y x 0 |
{0} | 0 0 0 1 |
4 4
o49 : Matrix R <--- R
|
i50 : relations N
o50 = {1} | 0 0 0 |
{1} | 0 0 0 |
{1} | 0 0 0 |
{0} | x y z |
4 3
o50 : Matrix R <--- R
|
The function
prune can be used to convert a subquotient module to a quotient module.
i51 : prune N
o51 = cokernel {2} | 0 0 0 z |
{2} | 0 0 0 x |
{2} | 0 0 0 -y |
{0} | z y x 0 |
4
o51 : R-module, quotient of R
|
We can use
resolution to compute a projective resolution of the cokernel of
f.
i52 : C = resolution cokernel f
1 3 3 1
o52 = R <-- R <-- R <-- R <-- 0
0 1 2 3 4
o52 : ChainComplex
|
To see the differentials we examine 'C.dd'.
i53 : C.dd
1 3
o53 = 0 : R <------------- R : 1
| x y z |
3 3
1 : R <-------------------- R : 2
{1} | -y -z 0 |
{1} | x 0 -z |
{1} | 0 x y |
3 1
2 : R <-------------- R : 3
{2} | z |
{2} | -y |
{2} | x |
1
3 : R <----- 0 : 4
0
o53 : ChainComplexMap
|
We can verify that
C is a complex by squaring the differential map.
i54 : C.dd^2 == 0
o54 = true
|
We can use
betti to see the degrees of the components of C.
i55 : betti C
0 1 2 3
o55 = total: 1 3 3 1
0: 1 3 3 1
o55 : BettiTally
|
Let's try a harder example. We can use
vars to create a sequence of variables.
i56 : R = ZZ/101[a .. r];
|
We use
genericMatrix to make a 3 by 6 generic matrix whose entries are drawn from the variables of the ring
R.
i57 : g = genericMatrix(R,a,3,6)
o57 = | a d g j m p |
| b e h k n q |
| c f i l o r |
3 6
o57 : Matrix R <--- R
|
Then we construct its cokernel with
cokernel.
i58 : M = cokernel g
o58 = cokernel | a d g j m p |
| b e h k n q |
| c f i l o r |
3
o58 : R-module, quotient of R
|
We may use
resolution to produce a projective resolution of it, and
time to report the time required.
i59 : time C = resolution M
-- used 0.00149353 seconds
3 6 15 18 6
o59 = R <-- R <-- R <-- R <-- R <-- 0
0 1 2 3 4 5
o59 : ChainComplex
|
As before, we may examine the degrees of its components, or display it.
i60 : betti C
0 1 2 3 4
o60 = total: 3 6 15 18 6
0: 3 6 . . .
1: . . . . .
2: . . 15 18 6
o60 : BettiTally
|
We can make a polynomial ring with 18
IndexedVariables.
i61 : S = ZZ/101[t_1 .. t_9, u_1 .. u_9];
|
We can use
genericMatrix to pack the variables into 3-by-3 matrices.
i62 : m = genericMatrix(S, t_1, 3, 3)
o62 = | t_1 t_4 t_7 |
| t_2 t_5 t_8 |
| t_3 t_6 t_9 |
3 3
o62 : Matrix S <--- S
|
i63 : n = genericMatrix(S, u_1, 3, 3)
o63 = | u_1 u_4 u_7 |
| u_2 u_5 u_8 |
| u_3 u_6 u_9 |
3 3
o63 : Matrix S <--- S
|
We may look at the matrix product.
i64 : m*n
o64 = | t_1u_1+t_4u_2+t_7u_3 t_1u_4+t_4u_5+t_7u_6 t_1u_7+t_4u_8+t_7u_9 |
| t_2u_1+t_5u_2+t_8u_3 t_2u_4+t_5u_5+t_8u_6 t_2u_7+t_5u_8+t_8u_9 |
| t_3u_1+t_6u_2+t_9u_3 t_3u_4+t_6u_5+t_9u_6 t_3u_7+t_6u_8+t_9u_9 |
3 3
o64 : Matrix S <--- S
|
Let's produce the equations generated by the equations that assert that m and n commute with each other. (See
flatten.)
i65 : j = flatten(m*n - n*m)
o65 = | t_4u_2+t_7u_3-t_2u_4-t_3u_7 t_2u_1-t_1u_2+t_5u_2+t_8u_3-t_2u_5-t_3u_8
-----------------------------------------------------------------------
t_3u_1+t_6u_2-t_1u_3+t_9u_3-t_2u_6-t_3u_9
-----------------------------------------------------------------------
-t_4u_1+t_1u_4-t_5u_4+t_4u_5+t_7u_6-t_6u_7 -t_4u_2+t_2u_4+t_8u_6-t_6u_8
-----------------------------------------------------------------------
-t_4u_3+t_3u_4+t_6u_5-t_5u_6+t_9u_6-t_6u_9
-----------------------------------------------------------------------
-t_7u_1-t_8u_4+t_1u_7-t_9u_7+t_4u_8+t_7u_9
-----------------------------------------------------------------------
-t_7u_2-t_8u_5+t_2u_7+t_5u_8-t_9u_8+t_8u_9 -t_7u_3-t_8u_6+t_3u_7+t_6u_8
-----------------------------------------------------------------------
|
1 9
o65 : Matrix S <--- S
|
Let's compute a Gröbner basis for the image of
j with
gb.
i66 : gb j
o66 = GroebnerBasis[status: done; S-pairs encountered up to degree 5]
o66 : GroebnerBasis
|
The resulting Gröbner basis contains a lot of information. We can get the generators of the basis, and even though we call upon
gb again, the computation will not be repeated.
i67 : generators gb j;
1 26
o67 : Matrix S <--- S
|
The semicolon prevents the matrix of generators from appearing on the screen, but the class of the matrix appears -- we see that there are 26 generators.
We can use
betti to see the degrees involved in the Gröbner basis.
i68 : betti gb j
0 1
o68 = total: 1 26
0: 1 .
1: . 8
2: . 12
3: . 5
4: . 1
o68 : BettiTally
|