2 Strings are being compared with != They should be using String.equals() https://github.com/imglib/imglib2-algorithm/blob/d6bb3aeaed7277a46b20e907eb7be1e720c2da04/src/main/java/net/imglib2/algorithm/math/Compute.java#L609 should be? if (! let.getVarName().equals(var.getName()) )