b2KIT

Inequality Grapher

Graph systems of linear and nonlinear inequalities with shaded feasible regions. Identify vertices and bounded regions.

Tested tool guide Tested browser tools Checked August 16, 2026

What Inequality Grapher does, with a checked example

This grapher shows where several inequalities are simultaneously true in the x-y plane. Enter linear or nonlinear conditions to display their boundary curves, shaded solution sets, and common feasible region. For polygonal systems, it can identify corner vertices and whether the overlap is bounded. The frequent mistake is reading the separate shaded sets as alternatives. A system uses their intersection: a point belongs only when it satisfies every entered inequality.

Worked example

A concrete input and expected output from the current implementation.

Input

x >= 0
y >= 0
x + y <= 4

Expected output

A bounded triangular feasible region, including its edges, with vertices (0, 0), (4, 0), and (0, 4).

The first two inequalities restrict solutions to the first quadrant. The line x + y = 4 meets the axes at (4, 0) and (0, 4), and the <= condition keeps the side containing (0, 0).

How the result is produced

1

Combining shaded sets

Each inequality divides the plane using its equality boundary, such as x + y = 4 for x + y <= 4. The satisfying side of that boundary is shaded. When several inequalities are entered, the feasible region is their overlap, since every condition must hold at once. Strict operators exclude their boundaries, while >= and <= include them.

2

Vertices and boundedness

For linear constraints, corner candidates occur where boundary lines intersect. A valid vertex must also satisfy every inequality in the system. A region is bounded when it cannot continue indefinitely in any direction. Nonlinear boundaries can instead enclose smooth regions, such as disks, for which a finite list of polygon-style vertices may not describe the shape.

Good uses

  • Sketch the feasible region defined by resource, capacity, and nonnegativity constraints before solving a linear programming exercise.
  • Check whether several half-planes overlap and list the corners of the resulting polygon.
  • Visualize nonlinear restrictions, such as the portion of a disk lying above a line.

Limits and checks

  • A region cut off by the visible plot edge may still be unbounded. Change the viewing range before concluding that the shading forms a closed feasible set.
  • A point on a boundary is feasible only when the corresponding operator includes equality. Replacing < with <= changes the solution set even if the shaded areas look nearly identical.
  • Vertices do not identify a maximum or minimum without an objective function. They describe the feasible geometry, and curved feasible regions may not have vertices at all.

Common questions

Why is a boundary point missing from the solution?

Check whether the inequality is strict. For x < 3, points with x = 3 are excluded because equality is not permitted. For x <= 3, those points are included. If several constraints meet at that boundary, the point must satisfy all of them, not merely the inequality whose line passes through it.

Does finding the vertices solve a linear programming problem?

No. The grapher can expose the feasible polygon and its vertices, but the constraints alone do not define what should be maximized or minimized. A specified linear objective can be evaluated at valid vertices, with separate attention to ties, infeasibility, and unbounded objectives. The feasible-region graph by itself is not a complete optimization result.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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