wgblas
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    Function idamax

    • Returns the 0-based index of the element with the largest absolute value, for a vector of doubles. Each element of x is split into a (hi, lo) double-double f32 pair (see splitDoubleDouble/f64.mjs) since WGSL has no f64 type; comparisons use the double-double pair directly (hi, falling back to lo on an exact tie), giving ~48 bits of discriminating precision — more than a single f32 (24 bits) but less than true f64 (52 bits). Ties are broken in favour of the lower index, matching CBLAS behaviour.

      import { init, cleanup } from "wgblas";
      import { idamax } from "wgblas/idamax";
      import { randomFloat64Array } from "wgblas/random";

      const device = await init();

      const n = 10;
      const x = randomFloat64Array(n, -10, 10);

      console.log("x:     ", x);
      const { index } = await idamax(device, n, x, 1);
      console.log("index: ", index);
      console.log("x[index]: ", x[index]);
      if (typeof process !== "undefined") cleanup();

      Browser (standalone HTML):

      <!doctype html>
      <html lang="en">
        <head>
          <meta charset="UTF-8" />
          <title>idamax — wgblas browser example</title>
          <script src="https://unpkg.com/wgblas/dist/wgblas.browser.js"></script>
        </head>
        <body>
          <pre id="out">Running…</pre>
          <script>
            const { init, idamax, randomFloat64Array, cleanup } = window.wgblas;

            (async () => {
              const device = await init();

              const n = 10;
              const x = randomFloat64Array(n, -10, 10);

              const { index } = await idamax(device, n, x, 1);

              document.getElementById("out").textContent =
                "x:        " + Array.from(x).map(v => v.toFixed(4)).join(", ") +
                "\nindex:    " + index +
                "\nx[index]: " + x[index].toFixed(4);

              cleanup();
            })();
          </script>
        </body>
      </html>

      Parameters

      • device: GPUDevice

        GPUDevice from init()

      • n: number

        number of elements (must be a positive integer)

      • x: Float64Array

        Float64Array input vector

      • incx: number

        stride for x (must be a positive integer)

      Returns Promise<{ index: number } | { gpuTimeMs: number; index: number }>

      0-based index of max |x[i]|

      Source code: idamax.mjs (L19)

    • Returns the 0-based index of the element with the largest absolute value. Ties are broken in favour of the lower index, matching CBLAS behaviour.

      import { init, cleanup } from "wgblas";
      import { idamax } from "wgblas/idamax";
      import { GpuVector } from "wgblas/classes/GpuVector";
      import { randomFloat64Array } from "wgblas/random";

      const device = await init();

      const n = 10;
      const x = randomFloat64Array(n, -10, 10);

      const xGpu = GpuVector.from(x);

      console.log("x:     ", x);

      const { index } = await idamax(device, n, xGpu, 1);
      console.log("index: ", index);

      xGpu.destroy();

      if (typeof process !== "undefined") cleanup();

      Parameters

      • device: GPUDevice

        GPUDevice from init()

      • n: number

        number of elements (must be a positive integer)

      • x: GpuVector

        Float64Array-backed GpuVector input vector

      • incx: number

        stride for x (must be a positive integer)

      Returns Promise<{ index: number } | { gpuTimeMs: number; index: number }>

      0-based index of max |x[i]|

      Source code: idamax.mjs (L19)

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