code: public SDVariable convertToVariable(@NonNull SDVariable constant) {
          Preconditions.checkState(constant.dataType().isFPType(), "Only floating point SDVariables can be converted to variables," +
                  " datatype of %s is %s", constant.getVarName(), constant.dataType());
          convertToVariables(Collections.singletonList(constant));
          return constant;
      }
docs: Convert the specified variable to a VARIABLE type SDVariable.<br>
  This can only be done for constants and placeholders, not ARRAY type variables (which are usually network activations).
  As a variable, this variable will modified during any subsequent training.<br>
  See also: {@link VariableType}
  
  @return This variable (now a variable type SDVariable)