same -- whether everything in a list is the same

Synopsis

Usage:

same L
Inputs:
- L, a list
Outputs:
- b, a Boolean

Description

i1 : same {1, 1, 1, 1}

o1 = true

i2 : same {1, 2, 1, 1}

o2 = false

The comparison is done with "===", which is quick, but not always intuitive. Here is a simple example of what can go wrong:

i3 : R = QQ[x,y,z];

i4 : L = {gcd{x,y}, x/x, 1}

o4 = {1, 1, 1}

o4 : List

i5 : same L

o5 = false

We can see the problem by asking Macaulay2 to display the class of each element of L. (Or use the function uniform, which returns whether or not the elements of a list are all of the same class.)

i6 : apply(L, class)

o6 = {R, frac R, ZZ}

o6 : List

i7 : uniform L

o7 = false

The first 1 is an element of the ring R, the second 1 is an element of the fraction field of R, and the third 1 is an integer. Thus Macaulay2 thinks of these three elements as being pairwise unequal, with respect to the operator "===".

For the programmer

The object same is a function closure.

same -- whether everything in a list is the same

Synopsis

Description

See also

For the programmer