Left side of equations, inequalities, relations, intervals, ranges and tables
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lhs(f
)
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 i
th
value in rhs(t)
corresponds to the i
th
key in lhs(t)
.
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)
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:
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 i
th value corresponds to the i
th
key:
bool(r = map(lhs(t), e>t[e]))
delete t,l,r:

An equation 
f