Yes, I didn't use sqrt(-1); I simply used I.

I have been using the 4 DMRG codes.

The code which calculates the ground-state energy ran, but yielded results which didn't account for the additional term which had an "I" in it.

In the code for calculating correlations, I tried to calculate Sx:Sy. I defined Sy in the models.xml file as:
<SITEOPERATOR name="Sy" site="x">
-(I/2)*(Splus(x)-Sminus(x))
</SITEOPERATOR>

The program doesn't run and I get the message: "Cannot evaluate expression Sy(i)".

On 28 September 2013 17:32, Matthias Troyer <troyer@phys.ethz.ch> wrote:

What code are you running?

sqrt(-1) will not work, by the way

On Sep 28, 2013, at 1:56 PM, pradeep thakur <pskvkthakur@gmail.com> wrote:

Dear Sir,

Thanks for your prompt response.

Yes, I did try I. The program for calculating the ground-state energy works as it did, without taking into account the new term (containing I) which I added in the models.xml file. I defined an Sy operator just like Sx. But Sy contains a sqrt(-1). The message I got was "Sy cannot be evaluated".

With regards,
Pradeep Thakur

On 28 September 2013 17:13, Matthias Troyer <troyer@phys.ethz.ch> wrote:

Have you tried I ?

On Sep 28, 2013, at 1:43 PM, pradeep thakur <pskvkthakur@gmail.com> wrote:

> Dear All,
>
> How can I introduce "i" (square-root of -1) into the model library (models.xml file)? I'm unable to define new site- and bond-operators which involve "i".
>
> Any help will be very much appreciated.
>
> With regards,
> Pradeep Thakur
> Dept. of Physics.,
> University of Pune,
> Pune, Maharashtra, INDIA.