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4.1 Generating Matrices

Operator: bunch elt_1 elt_2 … ¶

[elt_1, elt_2, …]

To collect any number of Jacal objects into a bunch, simply enclose them in square brackets. For example, to make the bunch whose elements are 1, 2, 4, type [1, 2, 4]. One can also nest bunches, for example, [1, [[1, 3], [2, 5]], [1, 4]]. Note however that the bunch whose only element is [1, 2, 3] is [1 2 3]. It is importance to notice that one has commas and the other doesn’t.

e3 : a:bunch(1, 2, 3);

e3: [1, 2, 3]

e4 : b:[a];

e4: [1  2  3]

e5 : c:[b];

e5: [[1, 2, 3]]

e6 : [[[1, 2, 3]]];

e6: [[1, 2, 3]]

Operator: flatten bnch ¶

Removes bunch nesting from bnch, returning a single bunch of the constituent expressions and equations.

e0 : flatten([a, [b, [c, d]], [5]]);

e0: [a, b, c, d, 5]

Command: ident n ¶

The command ident takes as argument a positive integer n and returns an nxn identity matrix. This is sometimes more convenient than obtaining this same matrix using the command scalarmatrix.

e6 : ident(4);

    [1  0  0  0]
    [          ]
    [0  1  0  0]
e6: [          ]
    [0  0  1  0]
    [          ]
    [0  0  0  1]

Command: scalarmatrix size entry ¶

The command scalarmatrix takes as inputs a positive integer size and an algebraic expression entry and returns an n * n diagonal matrix whose diagonal entries are all equal to entry, where n = size.

e1 : scalarmatrix(3, 6);

    [6  0  0]
    [       ]
e1: [0  6  0]
    [       ]
    [0  0  6]

Command: diagmatrix list ¶

The Jacal command diagmatrix takes as input a list of objects and returns the diagonal matrix having those objects as diagonal entries. In case one wants all of the diagonal entries to be equal, it is more convenient to use the command scalarmatrix.

e3 : diagmatrix(12,3,a,s^2);

    [12  0  0  0 ]
    [            ]
    [0   3  0  0 ]
e3: [            ]
    [0   0  a  0 ]
    [            ]
    [0   0  0   2]
    [          s ]

e4 : diagmatrix([1,2],2);

    [[1, 2]  0]
e4: [         ]
    [  0     2]

Command: sylvester poly_1 poly_2 var ¶

Here, poly_1 and poly_2 are polynomials and var is a variable. The function sylvester returns the matrix introduced by Sylvester (A Method of Determining By Mere Inspection the Derivatives from Two Equations of Any Degree, Phil.Mag. 16 (1840) pp. 132-135, Mathematical Papers, vol. I, pp. 54-57) for computing the resultant of the two polynomials poly_1 and poly_2 with respect to the variable var. If one wants to compute the resultant itself, one can simply use the command resultant with the same syntax.

e5 : sylvester(a0 + a1*x + a2*x^2 + a3*x^3, b0 + b1*x + b2*x^2, x);

    [a3  a2  a1  a0  0 ]
    [                  ]
    [0   a3  a2  a1  a0]
    [                  ]
e5: [b2  b1  b0  0   0 ]
    [                  ]
    [0   b2  b1  b0  0 ]
    [                  ]
    [0   0   b2  b1  b0]

Command: genmatrix function rows cols ¶

The function genmatrix takes as arguments a function of two variables and two positive integers, rows and cols. It returns a matrix with the indicated numbers of rows and columns in which the $(i,j)$th entry is obtained by evaluating function at $(i,j)$. The function may be defined in any of the ways available in Jacal, i.e previously by an explicit algebraic definition, by an explicit lambda expression or by an implicit lambda expression.

e4 : @1^2+@2^2;

                       2      2
e4: lambda([@1, @2], @1  + @2 )

e5 : genmatrix(e4,3,5);

    [2   5   10  17  26]
    [                  ]
e5: [5   8   13  20  29]
    [                  ]
    [10  13  18  25  34]