Horizontal Line Test in Set Theory
Consider a function with its corresponding graph as a subset of the Cartesian product . Consider the horizontal lines in :. The function f is injective if and only if each horizontal line intersects the graph at most once. In this case the graph is said to pass the horizontal line test. If any horizontal line intersects the graph more than once, the function fails the horizontal line test and is not injective.
A horizontal line is a straight line going right. A vertical line, however, is upwards (perpendicular mostly). Variations of the horizontal line test can be used to determine whether a function is surjective or bijective:
- The function f is surjective (i.e., onto) if and only if its graph intersects any horizontal line at LEAST once.
- f is bijective if and only if any horizontal line will intersect the graph EXACTLY once.
- Vertical line test
- Function (mathematics)
- Inverse (mathematics)
Read more about this topic: Horizontal Line Test
Famous quotes containing the words horizontal, line, test, set and/or theory:
“In bourgeois society, the French and the industrial revolution transformed the authorization of political space. The political revolution put an end to the formalized hierarchy of the ancien regimé.... Concurrently, the industrial revolution subverted the social hierarchy upon which the old political space was based. It transformed the experience of society from one of vertical hierarchy to one of horizontal class stratification.”
—Donald M. Lowe, U.S. historian, educator. History of Bourgeois Perception, ch. 4, University of Chicago Press (1982)
“For a woman to get a rewarding sense of total creation by way of the multiple monotonous chores that are her daily lot would be as irrational as for an assembly line worker to rejoice that he had created an automobile because he tightened a bolt.”
—Edith Mendel Stern (1901–1975)
“Tried by a New England eye, or the more practical wisdom of modern times, they are the oracles of a race already in its dotage; but held up to the sky, which is the only impartial and incorruptible ordeal, they are of a piece with its depth and serenity, and I am assured that they will have a place and significance as long as there is a sky to test them by.”
—Henry David Thoreau (1817–1862)
“The political horizon looks dark and lowering; but the people, under Providence, will set all right.”
—Abraham Lincoln (1809–1865)
“We commonly say that the rich man can speak the truth, can afford honesty, can afford independence of opinion and action;—and that is the theory of nobility. But it is the rich man in a true sense, that is to say, not the man of large income and large expenditure, but solely the man whose outlay is less than his income and is steadily kept so.”
—Ralph Waldo Emerson (1803–1882)