nd4j-backends/nd4j-api-parent/nd4j-api/src/main/java/org/nd4j/autodiff/samediff/SameDiff.java
public void putPlaceHolderForVariable(String varName, String... placeHolderVariables) {
        for (val placeHolderVariable : placeHolderVariables) {
            if (!variableMap.containsKey(placeHolderVariable)) {
                throw new ND4JIllegalStateException("No variable found for " + placeHolderVariable);
            }
        }


        List<String[]> placeHolders = placeHolderMap.get(varName);
        if (placeHolders == null) {
            placeHolders = new ArrayList<>();
            placeHolderMap.put(varName, placeHolders);
        }

        placeHolders.add(placeHolderVariables);
    }
public void putPlaceHolderForVariable(String varName, String... placeHolderVariables) {
        for (val placeHolderVariable : placeHolderVariables) {
            if (!variableMap.containsKey(placeHolderVariable)) {
                throw new ND4JIllegalStateException("No variable found for " + placeHolderVariable);
            }
        }


        List<String[]> placeHolders = placeHolderMap.get(varName);
        if (placeHolders == null) {
            placeHolders = new ArrayList<>();
            placeHolderMap.put(varName, placeHolders);
        }

        placeHolders.add(placeHolderVariables);
    }
Add one or or more place holder variables
for the given vertex id.
<p>
Note that if a vertex id in placeHolderVariables
isn't present in this samediff instance anyways,
an {@link ND4JIllegalStateException} is thrown

@param varName              the vertex id to add place holders for
@param placeHolderVariables the place holder variables