Operands of an object

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op(object, i)
op(object, i .. j)
op(object, [i1, i2, …])


op(object) returns all operands of the object.

op(object, i) returns the i-th operand.

op(object, i..j) returns the i-th to j-th operands.

MuPAD® objects are composed of simpler parts: the “operands”. The function op is the tool to decompose objects and to extract individual parts. The actual definition of an operand depends on the type of the object. The 'Background' section below explains the meaning for some of the basic data types.

op(object) returns a sequence of all operands except the 0-th one. This call is equivalent to op(object, 1..nops(object)). Cf. Example 1.

op(object, i) returns the i-th operand. Cf. Example 2.

op(object, i..j) returns the i-th to j-th operands as an expression sequence; i and j must be nonnegative integers with i smaller or equal to j. This sequence is equivalent to op(object, k) $k = i..j. Cf. Example 3.

op(object, [i1, i2, ...]) is an abbreviation for the recursive call op (... op ( op(object, i1) , i2) , ...) if i1, i2, ... are integers.

A call such as op(object, [i..j, i2]) with integers i < j corresponds to map(op(object, i..j), op, i2). Cf. Example 4.

op returns FAIL if the specified operand does not exist. Cf. Example 5.

Expressions of domain type DOM_EXPR, arrays, hfarrays, and floating point intervals have a 0-th operand.

  • For expressions, this is “the operator” connecting the other operands. In particular, for symbolic function calls, it is the name of the function.

  • For array and hfarrays, the 0-th operand is a sequence consisting of an integer (the dimension of the array) and a range for each array index.

  • For a floating-point interval, the value of the 0-th operand depends on the precise type of the interval: If the interval is a union of rectangles, the 0-th operand is hold(_union). If the interval is not a union and consists only of real numbers, the 0-th operand is hold(hull). In the remaining case of a rectangle with non-vanishing imaginary part, the 0-th operand is FAIL.

Other basic data types such as lists or sets do not have a 0-th operand. Cf. Example 6.

For library domains, op is overloadable. In the "op" method, the internal representation can be accessed with extop. It is sufficient to handle the cases op(x), op(x, i), and op(x, i..j) in the overloading method, the call op(x, [i1, i2, ...]) needs not be considered. Cf. Example 7.

op is not overloadable for kernel domains.


Example 1

The call op(object) returns all operands:

op([a, b, c, [d, e], x + y])

op(a + b + c^d)

op(f(x1, x2, x3))

Example 2

The call op(object, i) extracts a single operand:

op([a, b, c, [d, e], x + y], 4)

op(a + b + c^d, 3)

op(f(x1, x2, x3), 2)

Example 3

The call op(object, i..j) extracts a range of operands:

op([a, b, c, [d, e], x + y], 3..5)

op(a + b + c^d, 2..3)

op(f(x1, x2, x3), 2..3)

A range may include the 0-th operand if it exists:

op(a + b + c^d, 0..2)

op(f(x1, x2, x3), 0..2)

Example 4

The call op(object, [i1, i2, ...]) specifies suboperands:

op([a, b, c, [d, e], x + y], [4, 1])

op(a + b + c^d, [3, 2])

op(f(x1, x2, x3 + 17), [3, 2])

Also ranges of suboperands can be specified:

op([a, b, c, [d, e], x + y], [4..5, 2])

op(a + b + c^d, [2..3, 1])

op(f(x1, x2, x3 + 17), [2..3, 1])

Example 5

Nonexisting operands are returned as FAIL:

op([a, b, c, [d, e], x + y], 8), op(a + b + c^d, 4),
op(f(x1, x2, x3), 4)

Example 6

For expressions of type DOM_EXPR, the 0-th operand is “the operator” connecting the other operands:

op(a + b + c, 0), op(a*b*c, 0), op(a^b, 0), op(a[1, 2], 0)

For symbolic function calls, it is the name of the function:

op(f(x1, x2, x3), 0), op(sin(x + y), 0), op(besselJ(0, x), 0)

The 0-th operand of an array is a sequence consisting of the dimension of the array and a range for each array index:

op(array(3..100), 0)

op(array(1..2, 1..3, 2..4), 0)

op(hfarray(3..100), 0)

op(hfarray(1..2, 1..3, 2..4), 0)

No 0-th operand exists for other kernel domains:

op([1, 2, 3], 0), op({1, 2, 3}, 0), op(table(1 = y), 0)

Example 7

For library domains, op is overloadable. First, a new domain d is defined via newDomain. The "new" method serves for creating elements of this type. The internal representation of the domain is a list of all arguments of this "new" method:

d := newDomain("d"):  d::new := () -> new(dom, [args()]):

The "op" method of this domain is defined. It is to return the elements of a sorted copy of the internal list which is accessed via extop:

d::op := proc(x, i = null())
           local internalList;
           internalList := extop(x, 1);
           op(sort(internalList), i)

By overloading, this method is called when the operands of an object of type d are requested via op:

e := d(3, 7, 1):
op(e, 2);
op(e, 1..2)

delete d, e:

Example 8

Identifiers, integers, real floating-point numbers, character strings, and the Boolean constants are “atomic” objects. The only operand is the object itself:

op(x), op(17), op(0.1234), op("Hello World!")

For rational numbers, the operands are the numerator and the denominator:


For complex numbers, the operands are the real part and the imaginary part:

op(17 - 7/3*I)

Example 9

For sets, op returns the elements according to the internal order. Note that this order may differ from the ordering with which sets are printed on the screen:

s := {i^2 $ i = 1..19}


Indexed access to set elements uses the ordering visible on the screen:

s[1], s[2], s[3]

Note that access to set elements via op is much faster than indexed calls:

s := {sqrt(i) $ i = 1..500}:
time([op(s)])/time([s[i] $ i = 1..nops(s)]);

delete s:

Example 10

The operands of a list are its entries:

op([a, b, c, [d, e]])

op([[a11, a12], [a21, a22]], [2, 1])

Example 11

Internally, the operands of arrays and hfarrays form a “linear” sequence containing all entries:

op(array(1..2, 1..2, [[11, 12], [21, 22]]))

op(hfarray(1..2, 1..2, [[11, 12], [21, 22]]))

Undefined entries are returned as NIL:

op(array(1..2, 1..2))

Example 12

The operands of a table consist of equations relating the indices and the corresponding entries:

T := table((1, 2) = x + y, "diff(sin)" = cos, a = b)


delete T:

Example 13

Expression sequences are not flattened:

op((a, b, c), 2)

Note, however, that the arguments passed to op are evaluated. In the following call, evaluation of x flattens this object:

x := hold((1, 2), (3, 4)):  op(x, 1)

Use val to prevent simplification of x:

op(val(x), 1)

delete x:



An arbitrary MuPAD object

i, j

Nonnegative integers

i1, i2, …

Nonnegative integers or ranges of such integers

Return Values

sequence of operands or the requested operand. FAIL is returned if no corresponding operand exists.

Overloaded By



We explain the meaning of “operands” for some basic data types:

  • Identifiers, integers, real floating-point numbers, character strings, as well as the Boolean constants are “atomic” objects. They have only one operand: the object itself. Cf. Example 8.

  • A rational number of type DOM_RAT has two operands: the numerator and the denominator. Cf. Example 8.

  • A complex number of type DOM_COMPLEX has two operands: the real part and the imaginary part. Cf. Example 8.

  • The operands of a set are its elements.


    Note that the ordering of the elements as printed on the screen does not necessarily coincide with the internal ordering referred to by op. Cf. Example 9.

  • The operands of a list are its elements. Cf. Example 10.

  • The operands of arrays and hfarrays are its entries. Undefined entries are returned as NIL. Cf. Example 11 and Example 6.

  • The operands of tables are the equations associating an index with the corresponding entry. Cf. Example 12.

  • The operands of an expression sequence are its elements. Note that such sequences are not flattened by op. Cf. Example 13.

  • The operands of a symbolic function call such as f(x, y, ...) are the arguments x, y etc. The function name f is the 0-the operand.

  • In general, the operands of expressions of type DOM_EXPR are given by their internal representation. There is a 0-th operand (“the operator”) corresponding to the type of the expression. Internally, the operator is a system function, the expression corresponds to a function call. E.g., a + b + c has to be interpreted as _plus(a, b, c), a symbolic indexed call such as A[i, j] corresponds to _index(A, i, j). The name of the system function is the 0-th operand (i.e., _plus and _index in the previous examples), the arguments of the function call are the further operands.

See Also

MuPAD Functions