# replacements for commands and scripts from Macaulay

Macaulay2 aims to provide all of the functionality of Macaulay, but the names of the functions are not the same, and there are other differences. One major difference is the introduction of the notion of module, whereas in Macaulay, the pervasive concept was the matrix.

Here is a list of old Macaulay functions, together with pointers to functions in Macaulay2 that might be used to replace them.

Add matrices m and n, using result = m + n. In general, arithmetic in Macaulay2 is done using natural mathematical expressions. See +.

### betti <res>

Display the graded betti numbers of a chaincomplex or resolution C using betti C. See betti.

### chcalc <computation> [new hi deg]

Compute the Gröbner basis of m up to a given degree, using gb(m, DegreeLimit=>3). Similarly, if a computation in Macaulay2 has been halted by pressing <CTRL>-C, the computation can be restarted from where it left off, by giving the original command, e.g., gb m.

### cat <first var(0..numvars-1)> <result matrix>

Macaulay1 then also prompts for two lists of integers, say rows and cols. The resulting catalecticant matrix can be obtained in Macaulay2 in the following way.
 i1 : R = QQ[a..h] o1 = R o1 : PolynomialRing i2 : rows = {0,1,2} o2 = {0, 1, 2} o2 : List i3 : cols = {0,3} o3 = {0, 3} o3 : List i4 : result = map(R^3, 2, (i,j) -> R_(rows_i + cols_j)) o4 = | a d | | b e | | c f | 3 2 o4 : Matrix R <--- R

### characteristic <ring> [result integer]

To obtain the characteristic of a ring R, use char R. See char.

### codim <standard basis> [integer result]

When computing the codimension of an ideal or module M, a Gröbner basis is computed automatically, if needed. Use codim M.One use of this command in Macaulay1 was to compute the codimension of a partially computed Gröbner basis.

### coef <matrix> <result monoms> <result coefs> [variable list]

To obtain the matrices of monomials and their coefficients, use coefficients. The following example obtains the coefficients of the variable a (which is variable number 0)
 i5 : R = ZZ/101[a..d]; i6 : m = matrix{{a^2+a^2*c+a*b+3*d}} o6 = | a2c+a2+ab+3d | 1 1 o6 : Matrix R <--- R i7 : result = coefficients(m, Variables => {a}) o7 = (| a2 a 1 |, {2} | c+1 |) {1} | b | {0} | 3d | o7 : Sequence i8 : result_0 o8 = | a2 a 1 | 1 3 o8 : Matrix R <--- R i9 : result_1 o9 = {2} | c+1 | {1} | b | {0} | 3d | 3 1 o9 : Matrix R <--- R

### col_degree <matrix> <column> [result integer]

To obtain the degree of the i-th column of a matrix m, use (degrees source m)_i. See degrees. Note that in Macaulay2, one can use multi-degrees, so the result is a list of integers. Also all indices in Macaulay2 start at 0.
 i10 : R = QQ[a,b,Degrees=>{{1,0},{1,-1}}]; i11 : m = matrix{{a*b, b^2}} o11 = | ab b2 | 1 2 o11 : Matrix R <--- R i12 : (degrees source m)_0 o12 = {2, -1} o12 : List

### col_degs <matrix> [column degrees]

Compute the list of degrees of the columns of a matrix m using degrees source m. The result is a list of degrees. Each degree is itself a list of integers, since multi-degrees are allowed.

### commands

Using Macaulay2 in emacs, type the first few letters of a command, then hit <TAB>. The list of all commands starting with those letters will be displayed, or if there is only one, emacs will complete the typing for you.

### compress <matrix> <result matrix>

Remove columns of a matrix m which are entirely zero using compress m. See compress.

### concat <matrix> <matrix2> ... <matrix n>

Concatenate matrices m1, m2, ..., mn using m1 | m2 | ... | mn. See |. The main difference is that in Macaulay2 this command does not overwrite the first matrix.

### continue

In Macaulay2, one interrupts a computation using <CTRL>-C, as in Macaulay1. Restart the computation using the original command. For Gröbner basis and resolution commands, the computation starts off where it left off.

### contract <ideal> <ideal> <result matrix>

To contract the matrix n by the matrix m use contract(m,n). See contract. In Macaulay2, the arguments are not constrained to be matrices with one row.

### copy <existing matrix> <copy of matrix>

Since matrices in Macaulay2 are immutable objects, this command is no longer necessary. One can still make a copy of a matrix. For example
 i13 : R = ZZ/101[a..d] o13 = R o13 : PolynomialRing i14 : m = matrix{{a,b},{c,d}} o14 = | a b | | c d | 2 2 o14 : Matrix R <--- R i15 : copym = map(target m, source m, entries m) o15 = | a b | | c d | 2 2 o15 : Matrix R <--- R

### degree <standard basis> [integer codim] [integer degree]

When computing the degree of an ideal or module M, a Gröbner basis is computed automatically, if needed. Use degree M. Note that in Macaulay2, degree returns only the degree. Use codim M to obtain the codimension.One use of this command in Macaulay1 was to compute the degree of a partially computed Gröbner basis.

### determinants <matrix> <p> <result>

Use minors(p,m) to compute the ideal of p by p minors of the matrix m. See minors.

### diag <matrix> <result>

To make a diagonal matrix whose diagonal entries are taken from a matrix m, it is necessary to build the matrix directly, as in the following example.
 i16 : R = ZZ[a..d]; i17 : m = matrix{{a^2,b^3,c^4,d^5}} o17 = | a2 b3 c4 d5 | 1 4 o17 : Matrix R <--- R i18 : map(R^(numgens source m), source m, (i,j) -> if i === j then m_(0,i) else 0) o18 = | a2 0 0 0 | | 0 b3 0 0 | | 0 0 c4 0 | | 0 0 0 d5 | 4 4 o18 : Matrix R <--- R

### diff <ideal> <ideal> <result matrix>

To differentiate the matrix n by the matrix m use diff(m,n). See diff. In Macaulay2, the arguments are not constrained to be matrices with one row.

### dshift <matrix> <degree to shift by>

To shift the degrees of a matrix m by an integer d, use m ** (ring m)^{-d}. See **. Note that this returns a matrix with the degrees shifted, and does not modify the original matrix m. For example
 i19 : R = ZZ[a..d]; i20 : m = matrix{{a,b^2},{c^2,d^3}} o20 = | a b2 | | c2 d3 | 2 2 o20 : Matrix R <--- R i21 : betti m 0 1 o21 = total: 2 2 0: 2 . 1: . 1 2: . 1 o21 : BettiTally i22 : n = m ** R^{-1} o22 = {1} | a b2 | {1} | c2 d3 | 2 2 o22 : Matrix R <--- R i23 : betti n 0 1 o23 = total: 2 2 1: 2 . 2: . 1 3: . 1 o23 : BettiTally

### dsum <matrix> ... <matrix> <result>

To form the direct sum of matrices m1, m2, ..., mn, use m1 ++ m2 ++ ... ++ mn. See ++.

### elim <standard basis> <result matrix> [n]

To select the columns of the matrix m which lie in the subring defined by the first n slots of the monomial order being zero, use selectInSubring(n,m). Usually, one uses the value of 1 for n.

### ev <ideal> <matrix> <changed matrix>

In Macaulay2, one uses ring maps, or substitute to substitute variables. If m is a matrix in a ring R having n variables, and f is a 1 by n matrix over some ring, then use substitute(m,f) to perform the substitution. For example,
 i24 : R = QQ[a..d] o24 = R o24 : PolynomialRing i25 : S = QQ[s,t] o25 = S o25 : PolynomialRing i26 : m = matrix{{a^2-d, b*c}} o26 = | a2-d bc | 1 2 o26 : Matrix R <--- R i27 : f = matrix{{s^4,s^3*t,s*t^3,t^4}} o27 = | s4 s3t st3 t4 | 1 4 o27 : Matrix S <--- S i28 : substitute(m,f) o28 = | s8-t4 s4t4 | 1 2 o28 : Matrix S <--- S
In Macaulay2, one may also create and apply ring maps
 i29 : F = map(R,R,{b,c,d,a}) o29 = map(R,R,{b, c, d, a}) o29 : RingMap R <--- R i30 : m + F m + F F m + F F F m o30 = | a2+b2+c2+d2-a-b-c-d ab+bc+ad+cd | 1 2 o30 : Matrix R <--- R
Or one may substitute for only some variables
 i31 : substitute(m, {a=>1, b=>3}) o31 = | -d+1 3c | 1 2 o31 : Matrix R <--- R

### exit

Use exit to quit Macaulay2.

### fetch <matrix> <result matrix> [ones, default=zeros]

In order to bring a matrix m to a ring S which has ring variables of the same name, use substitute(m,S).
 i32 : R = ZZ[s,t] o32 = R o32 : PolynomialRing i33 : m = s^2+t^2 2 2 o33 = s + t o33 : R i34 : S = R[a..d] o34 = S o34 : PolynomialRing i35 : substitute(m,S) 2 2 o35 = s + t o35 : S

### flatten <matrix> <result ideal of entries>

In order to form a one row matrix with the entries of a matrix m, use flatten m. See flatten.

### forcestd <matrix> <result standard basis> [change of basis]

In order to inform the system that the columns of the matrix m form a Gröbner basis, use forceGB m. See forceGB.

### homog <matrix> <homog variable> <new matrix>

To homogenize a matrix m with respect to a variable x, use homogenize(m,x). One may also homogenize with respect to a given weight vector. See homogenize.

### ideal <resulting matrix>

To enter a one row matrix, use we may use the following method.
 i36 : R = ZZ[a..d] o36 = R o36 : PolynomialRing i37 : f = matrix{{a^2-b*c,3*b*c^4-1}} o37 = | a2-bc 3bc4-1 | 1 2 o37 : Matrix R <--- R
Remember that ideals, modules, and matrices are all different in Macaulay2. One can easily change between them, as in:
 i38 : J = ideal f 2 4 o38 = ideal (a - b*c, 3b*c - 1) o38 : Ideal of R i39 : generators J o39 = | a2-bc 3bc4-1 | 1 2 o39 : Matrix R <--- R i40 : image f o40 = image | a2-bc 3bc4-1 | 1 o40 : R-module, submodule of R i41 : cokernel f o41 = cokernel | a2-bc 3bc4-1 | 1 o41 : R-module, quotient of R

### iden <size> <result>

To make the identity map on a module F, use id_F, as in
 i42 : id_(R^4) o42 = | 1 0 0 0 | | 0 1 0 0 | | 0 0 1 0 | | 0 0 0 1 | 4 4 o42 : Matrix R <--- R
See id.

### if <integer> <label1> [<label2>]

For conditional execution, use the if-then or if-then-else statement

### int <name> <new value>

To assign a value to a variable in Macaulay2, use =. For example,
 i43 : myanswer = 2*(numgens R) - 1 o43 = 7
Warning: In Macaulay1, names of variables in rings, and user defined variables are completely separate. In Macaulay2, if you assign something to a ring variable, it will assume its new value.
 i44 : R = ZZ/31991[a..d] o44 = R o44 : PolynomialRing i45 : a o45 = a o45 : R i46 : a = 43 o46 = 43 i47 : a o47 = 43 i48 : use R o48 = R o48 : PolynomialRing i49 : a o49 = a o49 : R

### intersect <mat 1> ... <mat n> <result computation>

To intersect ideals, or submodules I1, I2, ..., In, use intersect(I1,I2,...,In). The main difference is that these values cannot be matrices, they must be ideals or submodules. A second difference is that the computation, if interrupted, must be restarted at the beginning. See intersect. For example,
 i50 : I = ideal(a^2-b,c-1,d^2-a*b) 2 2 o50 = ideal (a - b, c - 1, - a*b + d ) o50 : Ideal of R i51 : J = ideal(a*b-1, c*d-2) o51 = ideal (a*b - 1, c*d - 2) o51 : Ideal of R i52 : intersect(I,J) 2 3 o52 = ideal (c d - c*d - 2c + 2, a*b*c - a*b - c + 1, c*d - a*b*d + 2a*b - ----------------------------------------------------------------------- 2 2 2 2 2 2 c*d - 2d + d, a c*d - b*c*d - 2a + 2b, a b*d - b c*d - 2a b + a*c*d + ----------------------------------------------------------------------- 2 2 2 2 2 3 2 2 2b - a*d, a b - a*b*d - a*b + d , a b - a*b - a + b) o52 : Ideal of R

### is_zero <poly> <result integer: 1 if zero, else 0>

To decide whether a polynomial, matrix, ideal, etc., f is zero, use f == 0. The resulting value is a Boolean: either true, or false. See ==.

### jacob <ideal> <resulting jacobian> [variable list]

To find the Jacobian matrix of an ideal or one row matrixf, use jacobian f. If you only wish to differentiate with some of the variables, use diff instead. See jacobian.

### jump <label>

Macaulay2 has no go to statements. Instead, you should use the control structures.