Dear users, I need to use the Alps_mps_optim code to compute the expectation values of some complex operators e.g. string and parity operators. However, after modifying the model.xml file to define the operator of interest (following Michele Dolfi's earlier suggestion), I kept getting error messages indicating that I must have done somethings wrong in the model.xml file. Below is the relevant portion of the model.xml file that includes the modifications made by me: <SITEBASIS name="boson"> <PARAMETER name="rho" default="1" /> <PARAMETER name="theta" default="pi" /> !my modification <PARAMETER name="Nmax" default="infinity" /> <QUANTUMNUMBER name="N" min="0" max="Nmax" /> <OPERATOR name="bdag" matrixelement="sqrt(N+1)"> <CHANGE quantumnumber="N" change="1" /> </OPERATOR> <OPERATOR name="b" matrixelement="sqrt(N)"> <CHANGE quantumnumber="N" change="-1" /> </OPERATOR> <OPERATOR name="n" matrixelement="N" /> <OPERATOR name="n2" matrixelement="N*N" /> <OPERATOR name="dn" matrixelement="rho-N" /> <OPERATOR name="strireal" matrixelement="cos(theta*(rho-N))" /> !my modification <OPERATOR name="strimag" matrixelement="1j*sin(theta*(rho-N))" /> !my modification <OPERATOR name="string" matrixelement="cos(theta*(rho-N))+1j*sin(theta*(rho-N))" /> !my modification </SITEBASIS> Following is the result produced by the attempt to run the code with the modifications: Running task 1. This binary contains symmetries: nu1 MAQUIS repo r4143 Temporary storage enabled in /home/henry/Documents/ALPS_TEMP_DATA/storage_temp_ad178b56d3f6/ Restoring state. Will start again at site -1 in sweep 16 Exception thrown: Did not parse to end of string 'cos(theta*(rho-N))+1j*sin(theta*(rho-N))' henry@TheoreticalPhys-OAU:~$ The code ran when the "string" operator definition is removed, so that I believe that the problem is with my definition of the "string" operator. I will appreciate any assistance to help solve this problem. Thank you and best regards. Henry Otobrise, Dept. of Physics and Engineering Physics OAU, Ile-Ife, Nigeria.