659
edits
Cookbook: Difference between revisions
Jump to navigation
Jump to search
→Find if a number is even/odd
Carandraug (talk | contribs) (Created page with "An Octave cookbook. Each entry should go in a separate section and have the following subsection: problem, solution, discussion and maybe a see also. == Plotting == == User ...") |
Carandraug (talk | contribs) |
||
| Line 1: | Line 1: | ||
An Octave cookbook. Each entry should go in a separate section and have the following subsection: problem, solution, discussion and maybe a see also. | An Octave cookbook. Each entry should go in a separate section and have the following subsection: problem, solution, discussion and maybe a see also. | ||
== Mathematics == | |||
=== Find if a number is even/odd === | |||
==== Problem ==== | |||
You have a number, or an array or matrix of them, and want to know if any of them is an odd or even number, i.e., their parity. | |||
==== Solution ==== | |||
Check the remainder of a division by two. If the remainder is zero, the number is odd. | |||
mod (value, 2) ## 1 if odd, zero if even | |||
Since {{Codeline|mod()}} acceps a matrix, the following can be done: | |||
any (mod (values, 2)) ## true if at least one number in values is even | |||
all (mod (values, 2)) ## true if all numbers in values are odd | |||
any (!logical (mod (values, 2))) ## true if at least one number in values is even | |||
all (!logical (mod (values, 2))) ## true if all numbers in values are even | |||
==== Discussion ==== | |||
Since we are checking for the remainder of a division, the first choice would be to use {{Codeline|rem()}}. However, in the case of negative numbers {{Codeline|mod()}} will still return a positive number making it easier for comparisons. Another alternative is to use {{Codeline|bitand (X, 1)}} or {{Codeline|bitget (X, 1)}} but those are a bit slower. | |||
Note that this solution applies to integers only. Non-integers such as 1/2 or 4.201 are neither even nor odd. If the source of the numbers are unknown, such as user input, some sort of checking should be applied for NaN, Inf, non-integer values. | |||
==== See also ==== | |||
Find if a number is an integer. | |||
== Plotting == | == Plotting == | ||
== User input == | == User input == | ||