DM 42

[Thomas Okken]

(05-26-2017 12:52 PM)toml_12953 Wrote:  

(05-26-2017 07:34 AM)Paul Dale Wrote:  I'm fine with the 42S's behaviour. CPXRES and REALRES are required.

The question was more: should a calculator switch between real and complex mode automatically? It shouldn't unless told to. This works both ways: (0 + i)² should give (-1, 0) not -1.

Maybe for you it shouldn't but for me, it should always give an answer in either the real or complex plane as appropriate. If I could pick only one method, I'd have the calculator always give a numeric answer whether real or complex. If I was working a real-world problem and saw a complex result, I'd know there was no real solution. If the calculator always reported an error when given real inputs, there would be no way of knowing what the actual answer was.

Tom L

That's exactly what CPXRES mode does: with real inputs, you get real results if they exist, and complex results if necessary; with complex inputs, you always get complex results. This is the default mode on the HP-42S and in Free42, and, I assume, DM42 as well.