Function checkLossAndTargetCompatibility

tfjs-layers/src/engine/training.ts:230–269

* Validation on the compatibility of targes and loss functions. * * This helps prevent users from using loss functions incorrectly. * * @param targets `Array` of `tf.Tensor`s of targets. * @param lossFns `Array` of loss functions. * @param outputShapes `Array` of shapes of model outputs.

(
    targets: Tensor[], lossFns: LossOrMetricFn[], outputShapes: Shape[])

 * @param outputShapes `Array` of shapes of model outputs.
 */
function checkLossAndTargetCompatibility(
    targets: Tensor[], lossFns: LossOrMetricFn[], outputShapes: Shape[]) {
  // TODO(cais): Dedicated test coverage?
  const keyLosses = [
    losses.meanSquaredError, losses.binaryCrossentropy,
    losses.categoricalCrossentropy
  ];
  for (let i = 0; i < targets.length; ++i) {
    const y = targets[i];
    const loss = lossFns[i];
    const shape = outputShapes[i];
    if (loss == null) {
      continue;
    }
    if (loss === losses.categoricalCrossentropy) {
      if (y.shape[y.shape.length - 1] === 1) {
        throw new ValueError(
            `You are passing a target array of shape ${y.shape} while using ` +
            `a loss 'categorical_crossentropy'. 'categorical_crossentropy'` +
            `expects targets to be binary matrices (1s and 0s) of shape ` +
            `[samples, classes].`);
        // TODO(cais): Example code in error message.
      }
    }
    if (keyLosses.indexOf(loss) !== -1) {
      const slicedYShape = y.shape.slice(1);
      const slicedShape = shape.slice(1);
      for (let j = 0; j < slicedYShape.length; ++j) {
        const targetDim = slicedYShape[j];
        const outDim = slicedShape[j];
        if (outDim != null && targetDim !== outDim) {
          throw new ValueError(
              `A target Tensor with shape ${y.shape} was passed for an ` +
              `output of shape ${shape}, while using a loss function that ` +
              `expects targets to have the same shape as the output.`);
        }
      }
    }
  }
}

/**
 * Check inputs provided by the user.