diff --git a/regtest/basic/rt43/COLVAR.reference b/regtest/basic/rt43/COLVAR.reference
new file mode 100644
index 0000000000000000000000000000000000000000..25d32c01d6d3402e1c472b8d716915d44bfd11b9
--- /dev/null
+++ b/regtest/basic/rt43/COLVAR.reference
@@ -0,0 +1,6 @@
+#! FIELDS time rmsd0 rmsd1 rmsd2 rmsd3 rmsd4 stat.sqdevsum stat.corr stat.slope stat.intercept statn.sqdevsum statn.corr statn.slope statn.intercept statsq.sqdevsum
+ 0.000000 1.496 1.496 1.337 1.336 2.329 0.000 1.000 1.000 0.000 0.000 1.000 1.000 0.000 0.000
+ 0.050000 1.502 1.503 1.347 1.347 2.332 0.000 1.000 1.007 -0.019 0.000 1.000 1.007 -0.019 0.000
+ 0.100000 1.503 1.504 1.351 1.350 2.324 0.001 1.000 1.018 -0.037 0.001 1.000 1.018 -0.037 0.001
+ 0.150000 1.502 1.502 1.350 1.350 2.308 0.001 1.000 1.035 -0.060 0.001 1.000 1.035 -0.060 0.001
+ 0.200000 1.496 1.496 1.347 1.346 2.278 0.003 1.000 1.065 -0.098 0.003 1.000 1.065 -0.098 0.003
diff --git a/regtest/basic/rt43/Makefile b/regtest/basic/rt43/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..3703b27cea227aa053fb6d1d73f861e4384dbcee
--- /dev/null
+++ b/regtest/basic/rt43/Makefile
@@ -0,0 +1 @@
+include ../../scripts/test.make
diff --git a/regtest/basic/rt43/config b/regtest/basic/rt43/config
new file mode 100644
index 0000000000000000000000000000000000000000..4804b7f2a86c1dcb06f52d08f8dff331e318192f
--- /dev/null
+++ b/regtest/basic/rt43/config
@@ -0,0 +1,4 @@
+type=driver
+# this is to test a different name
+arg="--plumed plumed.dat --trajectory-stride 10 --timestep 0.005 --ixyz trajectory.xyz --dump-forces forces --dump-forces-fmt=%8.4f"
+extra_files="../../trajectories/trajectory.xyz"
diff --git a/regtest/basic/rt43/deriv.reference b/regtest/basic/rt43/deriv.reference
new file mode 100644
index 0000000000000000000000000000000000000000..ca14d348bcf00244134ca724bd16a3f488699479
--- /dev/null
+++ b/regtest/basic/rt43/deriv.reference
@@ -0,0 +1,26 @@
+#! FIELDS time parameter stat.sqdevsum stat.corr stat.slope stat.intercept statn.sqdevsum statn.corr statn.slope statn.intercept
+ 0.000000 0 -0.0004 0.0002 0.1489 -0.4381 -0.0004 0.0002 0.1489 -0.4381
+ 0.000000 1 0.0003 -0.0003 0.1480 -0.4365 0.0003 -0.0003 0.1480 -0.4365
+ 0.000000 2 -0.0008 0.0005 0.3792 -0.8063 -0.0008 0.0005 0.3792 -0.8063
+ 0.000000 3 0.0004 -0.0004 0.3789 -0.8057 0.0004 -0.0004 0.3789 -0.8057
+ 0.000000 4 0.0001 0.0000 -1.0550 1.4867 0.0001 0.0000 -1.0550 1.4867
+ 0.050000 0 0.0128 0.0026 0.1559 -0.4518 0.0128 0.0026 0.1559 -0.4518
+ 0.050000 1 0.0136 0.0021 0.1548 -0.4501 0.0136 0.0021 0.1548 -0.4501
+ 0.050000 2 0.0206 -0.0015 0.3806 -0.8127 0.0206 -0.0015 0.3806 -0.8127
+ 0.050000 3 0.0219 -0.0024 0.3802 -0.8121 0.0219 -0.0024 0.3802 -0.8121
+ 0.050000 4 0.0059 -0.0007 -1.0715 1.5198 0.0059 -0.0007 -1.0715 1.5198
+ 0.100000 0 0.0149 0.0030 0.1602 -0.4609 0.0149 0.0030 0.1602 -0.4609
+ 0.100000 1 0.0157 0.0024 0.1590 -0.4591 0.0157 0.0024 0.1590 -0.4590
+ 0.100000 2 0.0270 -0.0018 0.3887 -0.8280 0.0270 -0.0018 0.3887 -0.8280
+ 0.100000 3 0.0283 -0.0027 0.3883 -0.8274 0.0283 -0.0027 0.3883 -0.8274
+ 0.100000 4 -0.0099 -0.0009 -1.0961 1.5571 -0.0099 -0.0009 -1.0961 1.5571
+ 0.150000 0 0.0115 0.0023 0.1640 -0.4699 0.0115 0.0023 0.1640 -0.4699
+ 0.150000 1 0.0122 0.0017 0.1628 -0.4680 0.0122 0.0017 0.1628 -0.4680
+ 0.150000 2 0.0269 -0.0012 0.4030 -0.8529 0.0269 -0.0012 0.4030 -0.8529
+ 0.150000 3 0.0282 -0.0022 0.4026 -0.8523 0.0282 -0.0022 0.4026 -0.8523
+ 0.150000 4 -0.0415 -0.0006 -1.1325 1.6078 -0.0415 -0.0006 -1.1325 1.6078
+ 0.200000 0 -0.0005 0.0006 0.1700 -0.4839 -0.0005 0.0006 0.1700 -0.4839
+ 0.200000 1 0.0002 0.0000 0.1687 -0.4818 0.0002 0.0000 0.1687 -0.4818
+ 0.200000 2 0.0196 0.0002 0.4300 -0.8978 0.0196 0.0002 0.4300 -0.8978
+ 0.200000 3 0.0209 -0.0008 0.4296 -0.8972 0.0209 -0.0008 0.4296 -0.8972
+ 0.200000 4 -0.1020 -0.0001 -1.1982 1.6952 -0.1020 -0.0001 -1.1982 1.6952
diff --git a/regtest/basic/rt43/plumed.dat b/regtest/basic/rt43/plumed.dat
new file mode 100644
index 0000000000000000000000000000000000000000..3c656ff0307babff2546adebb9443886f44bd43e
--- /dev/null
+++ b/regtest/basic/rt43/plumed.dat
@@ -0,0 +1,22 @@
+rmsd0: RMSD TYPE=OPTIMAL REFERENCE=test0.pdb
+rmsd1: RMSD TYPE=OPTIMAL REFERENCE=test1.pdb
+rmsd2: RMSD TYPE=OPTIMAL REFERENCE=test2.pdb
+rmsd3: RMSD TYPE=OPTIMAL REFERENCE=test3.pdb
+rmsd4: RMSD TYPE=OPTIMAL REFERENCE=test4.pdb
+
+stat: STATS ARG=rmsd0,rmsd1,rmsd2,rmsd3,rmsd4 PARAMETERS=1.496,1.496,1.337,1.336,2.329
+statn: STATS ARG=rmsd0,rmsd1,rmsd2,rmsd3,rmsd4 PARAMETERS=1.496,1.496,1.337,1.336,2.329 NUMERICAL_DERIVATIVES
+statsq: STATS ARG=rmsd0,rmsd1,rmsd2,rmsd3,rmsd4 PARAMETERS=1.496,1.496,1.337,1.336,2.329 SQDEVSUM
+
+DUMPDERIVATIVES ARG=stat.*,statn.* STRIDE=1 FILE=deriv FMT=%8.4f
+
+PRINT ...
+ STRIDE=1
+ ARG=*
+ FILE=COLVAR FMT=%6.3f
+... PRINT
+
+
+ENDPLUMED
+
+text here should be ignored
diff --git a/regtest/basic/rt43/test0.pdb b/regtest/basic/rt43/test0.pdb
new file mode 100644
index 0000000000000000000000000000000000000000..eb3727de108b579ffd85bf6b03cc9c8e4181accd
--- /dev/null
+++ b/regtest/basic/rt43/test0.pdb
@@ -0,0 +1,15 @@
+ATOM 2 O ALA 2 -0.926 -2.447 -0.497 1.00 1.00 DIA O
+ATOM 4 HNT ALA 2 0.533 -0.396 1.184 1.00 1.00 DIA H
+ATOM 6 HT1 ALA 2 -0.216 -2.590 1.371 1.00 1.00 DIA H
+ATOM 7 HT2 ALA 2 -0.309 -1.255 2.315 1.00 1.00 DIA H
+ATOM 8 HT3 ALA 2 -1.480 -1.560 1.212 1.00 1.00 DIA H
+ATOM 9 CAY ALA 2 -0.096 2.144 -0.669 1.00 1.00 DIA C
+ATOM 10 HY1 ALA 2 0.871 2.385 -0.588 1.00 1.00 DIA H
+ATOM 12 HY3 ALA 2 -0.520 2.679 -1.400 1.00 1.00 DIA H
+ATOM 14 OY ALA 2 -1.139 0.931 -0.973 1.00 1.00 DIA O
+ATOM 16 HN ALA 2 1.713 1.021 -0.873 1.00 1.00 DIA H
+ATOM 18 HA ALA 2 0.099 -0.774 -2.218 1.00 1.00 DIA H
+ATOM 19 CB ALA 2 2.063 -1.223 -1.276 1.00 1.00 DIA C
+ATOM 20 HB1 ALA 2 2.670 -0.716 -2.057 1.00 1.00 DIA H
+ATOM 21 HB2 ALA 2 2.556 -1.051 -0.295 1.00 1.00 DIA H
+ATOM 22 HB3 ALA 2 2.070 -2.314 -1.490 1.00 1.00 DIA H
diff --git a/regtest/basic/rt43/test1.pdb b/regtest/basic/rt43/test1.pdb
new file mode 100644
index 0000000000000000000000000000000000000000..924aa4b057f24d6467f39ff489e249b06faf8de8
--- /dev/null
+++ b/regtest/basic/rt43/test1.pdb
@@ -0,0 +1,15 @@
+ATOM 2 O ALA 2 -0.926 -2.447 -0.497 1.00 1.01 DIA O
+ATOM 4 HNT ALA 2 0.533 -0.396 1.184 1.00 1.00 DIA H
+ATOM 6 HT1 ALA 2 -0.216 -2.590 1.371 1.00 1.00 DIA H
+ATOM 7 HT2 ALA 2 -0.309 -1.255 2.315 1.00 1.00 DIA H
+ATOM 8 HT3 ALA 2 -1.480 -1.560 1.212 1.00 1.00 DIA H
+ATOM 9 CAY ALA 2 -0.096 2.144 -0.669 1.00 1.00 DIA C
+ATOM 10 HY1 ALA 2 0.871 2.385 -0.588 1.00 1.00 DIA H
+ATOM 12 HY3 ALA 2 -0.520 2.679 -1.400 1.00 1.00 DIA H
+ATOM 14 OY ALA 2 -1.139 0.931 -0.973 1.00 1.00 DIA O
+ATOM 16 HN ALA 2 1.713 1.021 -0.873 1.00 1.00 DIA H
+ATOM 18 HA ALA 2 0.099 -0.774 -2.218 1.00 1.00 DIA H
+ATOM 19 CB ALA 2 2.063 -1.223 -1.276 1.00 0.99 DIA C
+ATOM 20 HB1 ALA 2 2.670 -0.716 -2.057 1.00 1.00 DIA H
+ATOM 21 HB2 ALA 2 2.556 -1.051 -0.295 1.00 1.00 DIA H
+ATOM 22 HB3 ALA 2 2.070 -2.314 -1.490 1.00 1.00 DIA H
diff --git a/regtest/basic/rt43/test2.pdb b/regtest/basic/rt43/test2.pdb
new file mode 100644
index 0000000000000000000000000000000000000000..f2585025b36c688adfab6aee461070d572635f66
--- /dev/null
+++ b/regtest/basic/rt43/test2.pdb
@@ -0,0 +1,15 @@
+ATOM 2 O ALA 2 -0.926 -2.447 -0.497 1.10 1.10 DIA O
+ATOM 4 HNT ALA 2 0.533 -0.396 1.184 1.00 1.00 DIA H
+ATOM 6 HT1 ALA 2 -0.216 -2.590 1.371 1.00 1.00 DIA H
+ATOM 7 HT2 ALA 2 -0.309 -1.255 2.315 1.00 1.00 DIA H
+ATOM 8 HT3 ALA 2 -1.480 -1.560 1.212 5.00 5.00 DIA H
+ATOM 9 CAY ALA 2 -0.096 2.144 -0.669 1.00 1.00 DIA C
+ATOM 10 HY1 ALA 2 0.871 2.385 -0.588 1.00 1.00 DIA H
+ATOM 12 HY3 ALA 2 -0.520 2.679 -1.400 1.00 1.00 DIA H
+ATOM 14 OY ALA 2 -1.139 0.931 -0.973 0.00 0.00 DIA O
+ATOM 16 HN ALA 2 1.713 1.021 -0.873 1.00 1.00 DIA H
+ATOM 18 HA ALA 2 0.099 -0.774 -2.218 0.00 0.00 DIA H
+ATOM 19 CB ALA 2 2.063 -1.223 -1.276 1.00 1.00 DIA C
+ATOM 20 HB1 ALA 2 2.670 -0.716 -2.057 1.00 1.00 DIA H
+ATOM 21 HB2 ALA 2 2.556 -1.051 -0.295 1.00 1.00 DIA H
+ATOM 22 HB3 ALA 2 2.070 -2.314 -1.490 1.00 1.00 DIA H
diff --git a/regtest/basic/rt43/test3.pdb b/regtest/basic/rt43/test3.pdb
new file mode 100644
index 0000000000000000000000000000000000000000..4b04045e2a4baed871505c0e074d29d0065ab0fb
--- /dev/null
+++ b/regtest/basic/rt43/test3.pdb
@@ -0,0 +1,15 @@
+ATOM 2 O ALA 2 -0.926 -2.447 -0.497 1.10 1.10 DIA O
+ATOM 4 HNT ALA 2 0.533 -0.396 1.184 1.00 1.00 DIA H
+ATOM 6 HT1 ALA 2 -0.216 -2.590 1.371 1.00 1.00 DIA H
+ATOM 7 HT2 ALA 2 -0.309 -1.255 2.315 1.00 1.00 DIA H
+ATOM 8 HT3 ALA 2 -1.480 -1.560 1.212 5.00 5.01 DIA H
+ATOM 9 CAY ALA 2 -0.096 2.144 -0.669 1.00 1.00 DIA C
+ATOM 10 HY1 ALA 2 0.871 2.385 -0.588 1.00 1.00 DIA H
+ATOM 12 HY3 ALA 2 -0.520 2.679 -1.400 1.00 1.00 DIA H
+ATOM 14 OY ALA 2 -1.139 0.931 -0.973 0.00 0.00 DIA O
+ATOM 16 HN ALA 2 1.713 1.021 -0.873 1.00 1.00 DIA H
+ATOM 18 HA ALA 2 0.099 -0.774 -2.218 0.00 0.00 DIA H
+ATOM 19 CB ALA 2 2.063 -1.223 -1.276 1.00 1.00 DIA C
+ATOM 20 HB1 ALA 2 2.670 -0.716 -2.057 1.00 1.00 DIA H
+ATOM 21 HB2 ALA 2 2.556 -1.051 -0.295 1.00 1.00 DIA H
+ATOM 22 HB3 ALA 2 2.070 -2.314 -1.490 1.00 1.00 DIA H
diff --git a/regtest/basic/rt43/test4.pdb b/regtest/basic/rt43/test4.pdb
new file mode 100644
index 0000000000000000000000000000000000000000..455f79f38cdf72be596b1883f5be162bf37d5983
--- /dev/null
+++ b/regtest/basic/rt43/test4.pdb
@@ -0,0 +1,15 @@
+ATOM 2 O ALA 2 -0.926 -2.447 -0.497 1.00 0.00 DIA O
+ATOM 4 HNT ALA 2 0.533 -0.396 1.184 1.00 0.00 DIA H
+ATOM 6 HT1 ALA 2 -0.216 -2.590 1.371 1.00 0.00 DIA H
+ATOM 7 HT2 ALA 2 -0.309 -1.255 2.315 1.00 0.00 DIA H
+ATOM 8 HT3 ALA 2 -1.480 -1.560 1.212 1.00 0.00 DIA H
+ATOM 9 CAY ALA 2 -0.096 2.144 -0.669 1.00 0.00 DIA C
+ATOM 10 HY1 ALA 2 0.871 2.385 -0.588 1.00 0.00 DIA H
+ATOM 12 HY3 ALA 2 -0.520 2.679 -1.400 1.00 0.00 DIA H
+ATOM 14 OY ALA 2 -1.139 0.931 -0.973 0.00 1.00 DIA O
+ATOM 16 HN ALA 2 1.713 1.021 -0.873 0.00 1.00 DIA H
+ATOM 18 HA ALA 2 0.099 -0.774 -2.218 0.00 1.00 DIA H
+ATOM 19 CB ALA 2 2.063 -1.223 -1.276 0.00 1.00 DIA C
+ATOM 20 HB1 ALA 2 2.670 -0.716 -2.057 0.00 1.00 DIA H
+ATOM 21 HB2 ALA 2 2.556 -1.051 -0.295 0.00 1.00 DIA H
+ATOM 22 HB3 ALA 2 2.070 -2.314 -1.490 0.00 1.00 DIA H
diff --git a/src/function/Stats.cpp b/src/function/Stats.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..c3f9035bff321a7e9d22ae33eaa813f8ed4b2365
--- /dev/null
+++ b/src/function/Stats.cpp
@@ -0,0 +1,166 @@
+/* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Copyright (c) 2011-2015 The plumed team
+ (see the PEOPLE file at the root of the distribution for a list of names)
+
+ See http://www.plumed-code.org for more information.
+
+ This file is part of plumed, version 2.
+
+ plumed is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ plumed is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with plumed. If not, see <http://www.gnu.org/licenses/>.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
+#include "Function.h"
+#include "ActionRegister.h"
+
+#include <cmath>
+
+using namespace std;
+
+namespace PLMD{
+namespace function{
+
+//+PLUMEDOC FUNCTION STATS
+/*
+
+\endverbatim
+
+*/
+//+ENDPLUMEDOC
+
+
+class Stats :
+ public Function
+{
+ std::vector<double> parameters;
+ bool sqdonly;
+public:
+ explicit Stats(const ActionOptions&);
+ void calculate();
+ static void registerKeywords(Keywords& keys);
+};
+
+
+PLUMED_REGISTER_ACTION(Stats,"STATS")
+
+void Stats::registerKeywords(Keywords& keys){
+ Function::registerKeywords(keys);
+ keys.use("ARG");
+ keys.add("compulsory","PARAMETERS","0.0","the parameters of the arguments in your function");
+ keys.addFlag("SQDEVSUM",false,"calculates only SQDEVSUM");
+}
+
+Stats::Stats(const ActionOptions&ao):
+Action(ao),
+Function(ao),
+parameters(getNumberOfArguments(),0.0),
+sqdonly(false)
+{
+ parseVector("PARAMETERS",parameters);
+ if(parameters.size()!=static_cast<unsigned>(getNumberOfArguments()))
+ error("Size of PARAMETERS array should be the same as number for arguments");
+
+ parseFlag("SQDEVSUM",sqdonly);
+
+
+ addComponentWithDerivatives("sqdevsum");
+ componentIsNotPeriodic("sqdevsum");
+ if(!sqdonly) {
+ addComponentWithDerivatives("corr");
+ componentIsNotPeriodic("corr");
+ addComponentWithDerivatives("slope");
+ componentIsNotPeriodic("slope");
+ addComponentWithDerivatives("intercept");
+ componentIsNotPeriodic("intercept");
+ }
+
+ checkRead();
+}
+
+void Stats::calculate()
+{
+ if(sqdonly) {
+
+ double nsqd = 0.;
+ Value* valuea=getPntrToComponent("sqdevsum");
+ for(unsigned i=0;i<parameters.size();++i){
+ double dev = getArgument(i)-parameters[i];
+ setDerivative(valuea,i,2.*dev);
+ nsqd += dev*dev;
+ }
+ valuea->set(nsqd);
+
+ } else {
+
+ double scx=0., scx2=0., scy=0., scy2=0., scxy=0.;
+
+ for(unsigned i=0;i<parameters.size();++i){
+ scx += getArgument(i);
+ scx2 += getArgument(i)*getArgument(i);
+ scy += parameters[i];
+ scy2 += parameters[i]*parameters[i];
+ scxy += getArgument(i)*parameters[i];
+ }
+
+ double ns = parameters.size();
+
+ double num = ns*scxy - scx*scy;
+ double idev2x = 1./(ns*scx2-scx*scx);
+ double idevx = sqrt(idev2x);
+ double idevy = 1./sqrt(ns*scy2-scy*scy);
+
+ /* sd */
+ double nsqd = scx2 + scy2 - 2.*scxy;
+ /* correlation */
+ double correlation = num * idevx * idevy;
+ /* slope and intercept */
+ double slope = num * idev2x;
+ double inter = (scy - slope * scx)/ns;
+
+ Value* valuea=getPntrToComponent("sqdevsum");
+ Value* valueb=getPntrToComponent("corr");
+ Value* valuec=getPntrToComponent("slope");
+ Value* valued=getPntrToComponent("intercept");
+
+ valuea->set(nsqd);
+ valueb->set(correlation);
+ valuec->set(slope);
+ valued->set(inter);
+
+ /* derivatives */
+ for(unsigned i=0;i<parameters.size();++i){
+ double common_d1 = (ns*parameters[i]-scy)*idevx;
+ double common_d2 = num*(ns*getArgument(i)-scx)*idev2x*idevx;
+ double common_d3 = common_d1 - common_d2;
+
+ /* sqdevsum */
+ double sq_der = 2.*(getArgument(i)-parameters[i]);
+ /* correlation */
+ double co_der = common_d3*idevy;
+ /* slope */
+ double sl_der = (common_d1-2.*common_d2)*idevx;
+ /* intercept */
+ double int_der = -(slope+ scx*sl_der)/ns;
+
+ setDerivative(valuea,i,sq_der);
+ setDerivative(valueb,i,co_der);
+ setDerivative(valuec,i,sl_der);
+ setDerivative(valued,i,int_der);
+ }
+
+ }
+}
+
+}
+}
+
+