ml-gsd/lib/algorithms/xGetCrossZeroPoints.js

Global Spectral Deconvolution

/**
 * Finds the indices where the first derivative crosses zero (sign change),
 * which are potential peak positions. This function does not detect zero-crossings
 * in regions with consecutive zero values in the derivative (flat regions).
 *
 * @param input - Object containing the y values and their first derivative (dY).
 * @returns Array of indices where the first derivative crosses zero (excluding consecutive zeros).
 */
export function xGetCrossZeroPoints(input) {
    const { y, dY } = input;
    const crossDy = [];
    for (let i = 1; i < y.length - 1; ++i) {
        if (isLessAndGreaterThanZero(dY[i], dY[i + 1])) {
            // push the index of the element closer to zero
            crossDy.push(Math.abs(dY[i]) < Math.abs(dY[i + 1]) ? i : i + 1);
        }
        else if (
        // Handle exact zero
        dY[i] === 0 &&
            isLessAndGreaterThanZero(dY[i - 1], dY[i + 1])) {
            crossDy.push(i);
        }
    }
    return crossDy;
}
function isLessAndGreaterThanZero(back, next) {
    return (back < 0 && next > 0) || (back > 0 && next < 0);
}
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