TheAlgorithms/Java · error · IllegalArgumentException

persistence must be in (0, 1]

Error message

persistence must be in (0, 1]

What it means

Thrown by generatePerlinNoise when the persistence parameter falls outside the open-closed interval (0, 1]. Persistence is the per-octave amplitude multiplier used when blending noise layers; values outside (0, 1] break the geometric amplitude series (a persistence of 0 zeroes every layer, and >1 unbounds the amplitude sum). The check uses !(persistence > 0f && persistence <= 1f) specifically to reject NaN as well, since NaN comparisons always evaluate false.

Source

Thrown at src/main/java/com/thealgorithms/others/PerlinNoise.java:62

     *
     * @param width       width of the noise array (columns)
     * @param height      height of the noise array (rows)
     * @param octaveCount number of octaves (layers) to blend; must be >= 1
     * @param persistence per-octave amplitude multiplier in (0, 1]
     * @param seed        seed for the random base grid
     * @return a {@code width x height} array containing blended noise values in [0,
     *         1]
     */
    static float[][] generatePerlinNoise(int width, int height, int octaveCount, float persistence, long seed) {
        if (width <= 0 || height <= 0) {
            throw new IllegalArgumentException("width and height must be > 0");
        }

        if (octaveCount < 1) {
            throw new IllegalArgumentException("octaveCount must be >= 1");
        }
        if (!(persistence > 0f && persistence <= 1f)) { // using > to exclude 0 and NaN
            throw new IllegalArgumentException("persistence must be in (0, 1]");
        }
        final float[][] base = createBaseGrid(width, height, seed);
        final float[][][] layers = createLayers(base, width, height, octaveCount);
        return blendAndNormalize(layers, width, height, persistence);
    }

    /** Create the base random lattice values in [0,1). */
    static float[][] createBaseGrid(int width, int height, long seed) {
        final float[][] base = new float[width][height];
        Random random = new Random(seed);
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
                base[x][y] = random.nextFloat();
            }
        }
        return base;
    }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Pass a persistence strictly greater than 0 and at most 1; typical terrain/noise values are 0.5 to 0.8.
2. If persistence is derived from user input or config, clamp and validate it in range before calling generatePerlinNoise.
3. Guard against NaN explicitly: check !Float.isNaN(persistence) before the call if the value can originate from untrusted arithmetic.
4. If you intended a flat (zero-blend) noise field, that is not representable here — use a single octave with persistence 1 instead.

Example fix

// before
float[][] n = PerlinNoise.generatePerlinNoise(256, 256, 5, 0f, 42L);
// after
float[][] n = PerlinNoise.generatePerlinNoise(256, 256, 5, 0.5f, 42L);

private static void validatePersistence(float p) {
    if (Float.isNaN(p) || !(p > 0f && p <= 1f)) {
        throw new IllegalArgumentException("persistence must be in (0, 1], got " + p);
    }
}
// call before generatePerlinNoise

When it happens

Trigger: Calling generatePerlinNoise(width, height, octaveCount, persistence, seed) with persistence == 0f, persistence > 1f, or persistence == Float.NaN. Also triggered by accidentally passing an integer 0 or a negative value where a float persistence is expected.

Common situations: Supplying 0 because the field was uninitialized, defaulting persistence to 0 in a config object, passing a percentage like 50 (meaning 50%) instead of 0.5, or propagating Float.NaN from a prior computation that divided by zero or parsed a bad value.

Related errors

• Orbiting mass and radius must be positive.
• Natural frequency must be positive.
• Damping coefficient must be non-negative.
• State must be a non-null array of length 2.
• Time step must be positive.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/61fe3722778544bb. Report an issue: GitHub.