# [AMBER] Data set math gives "size is 0"

From: Chunsheng Lin via AMBER <amber.ambermd.org>
Date: Fri, 23 Sep 2022 12:03:32 +0800 (CST)

Dear Colleagues,

I want to calculate two bond lengths as well as their differences with cpptraj. My cpptraj.in file is as following:
trajin a18.nc
distance dT1_T2 .683 .684 out a18.txt
distance dT2_T3 .684 .664 out a18.txt
cv = dT1_T2 - dT2_T3
write a18.txt cv

However, cpptraj gives such results:
BEGIN TRAJECTORY PROCESSING:
.....................................................
ACTION SETUP FOR PARM 'a18.prmtop' (2 actions):
0: [distance dT1_T2 .683 .684 out a18.txt]
.683 (1 atoms) to .684 (1 atoms), imaged.
1: [distance dT2_T3 .684 .664 out a18.txt]
.684 (1 atoms) to .664 (1 atoms), imaged.
----- a18.nc (1-6204, 1) -----
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Complete.

Read 6204 frames and processed 6204 frames.
TIME: Avg. throughput= 17658.8126 frames / second.

ACTION OUTPUT:
TIME: Analyses took 0.0000 seconds.

DATASETS (3 total):
dT1_T2 "dT1_T2" (double, distance), size is 6204
dT2_T3 "dT2_T3" (double, distance), size is 6204
cv "cv" (double), size is 0

DATAFILES (1 total):
a18.txt (Standard Data File): dT1_T2 dT2_T3
--------------------------
The resulted file a18.txt has only dT1_T2 and dT2_T3, and no cv. What is the problem? Why the data set math result "cv" size is 0?

Best regards,
Chunsheng

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Received on Thu Sep 22 2022 - 21:30:03 PDT
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