What is the precise specification of `broadcast` in ND4j / DL4j?

问题

What is the precise definition of INDArray.broadcast(long...) in ND4j?

The description of both methods only says "Broadcasts this ndarray to be the specified shape", and does not explain the requirements for acceptable shapes to be broadcast.

The following code (meant to broadcast an ndarray to a shape of an extra first dimension of length 3) does not work:

INDArray array = Nd4j.create(new double[] {1.,2.,3.,4.}, new int[] {2,2}, 'c');
System.out.println("array: " + array);
System.out.println("array.broadcast(3,2,2): " + array.broadcast(3,2,2));

I had previously tried broadcasting an array of shape (4) to (3,4) and that worked. I tried (2,2) to (2,2,3) and got an error about incompatible shapes. In the (2,2) to (3,2,2) above I do not get an error about incompatible shapes, so I guess they are compatible and it should work, but I get the following error:

Error at [D:/jenkins/ws/dl4j-deeplearning4j-1.0.0-beta4-windows-x86_64-cpu/libnd4j/include/ops/declarable/generic/transforms/tile.cpp:83:0]:
TILE op: this op requires repeats vector, either as IArgs or second array with length equal to rank of input array to be tiled !
Exception in thread "main" java.lang.RuntimeException: Op [tile] execution failed
    at org.nd4j.linalg.cpu.nativecpu.ops.NativeOpExecutioner.exec(NativeOpExecutioner.java:1645)
    at org.nd4j.linalg.api.ops.executioner.DefaultOpExecutioner.execAndReturn(DefaultOpExecutioner.java:714)
    at org.nd4j.linalg.api.ndarray.BaseNDArray.broadcast(BaseNDArray.java:5451)
    at org.nd4j.linalg.api.ndarray.BaseNDArray.broadcast(BaseNDArray.java:5465)
    at com.sri.ai.praise.core.representation.interfacebased.factor.core.table.NDArraySandbox.main(NDArraySandbox.java:21)
Caused by: java.lang.RuntimeException: Op validation failed
    at org.nd4j.nativeblas.Nd4jCpu$NativeOps.execCustomOp(Native Method)
    at org.nd4j.linalg.cpu.nativecpu.ops.NativeOpExecutioner.exec(NativeOpExecutioner.java:2045)
    at org.nd4j.linalg.cpu.nativecpu.ops.NativeOpExecutioner.exec(NativeOpExecutioner.java:1637)
    ... 4 more

来源：https://stackoverflow.com/questions/60143939/what-is-the-precise-specification-of-broadcast-in-nd4j-dl4j

标签

java

numpy-broadcasting

dl4j

nd4j