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Left side of equations, inequalities, relations, intervals, ranges and tables

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lhs(f) returns the left side of f.

The call lhs(f) is equivalent to the direct call op(f,1), of the operand function op, if f is not a table.

If t is a table, the call lhs(t) returns the list of keys of the table (left side). Note that the ith value in rhs(t) corresponds to the ith key in lhs(t).


Example 1

Extract the left sides of various objects:

lhs(x = sin(2)), lhs(3.14 <> PI), lhs(x + 3 < 2*y)

The operands of an expression depend on its internal representation. In particular, a "greater" relation is always converted to the corresponding "less" relation:

y > -infinity;
lhs(y > -infinity)

y >= 4;
lhs(y >= 4)

Example 2

Extract the left sides of the solution of the following system:

s := solve({x + y = 1, 2*x - 3*y = 2})

map(op(s), lhs)

Calls to lhs can be easier to read than the equivalent calls to the operand function op:

map(op(s), op, 1)

However, direct calls to op must be preferred inside procedures for higher efficiency.

delete s:

Example 3

Extract the keys (left side) and values (right side) from a table:

t := table(1=2, 4=PI, 5=5.6, 19=1/2):
l := lhs(t);

r := rhs(t);

Note that the ith value corresponds to the ith key:

bool(r = map(lhs(t), e->t[e]))

delete t,l,r:



An equation x = y, an inequality x <> y, a relation x < y, a relation x <= y, an "is element of"-relation x in y, an interval x...y, a range x..y, or a table table(x=y,...).

Overloaded By


See Also

MuPAD Functions

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