# [gmx-users] g_analyze errors

Alex alexbioinfo at yahoo.com
Tue Nov 1 18:29:22 CET 2011

```Dear all,

I run a NPT equilibration (1 ns - 1000 steps) and then I drew pressure graph
using g_energy.
I've tried to run the following command

g_analyze -f pressure.xvg  -av average.xvg -ee errest.xvg

****************G_ANALYZE PRESSURE*******************
But I get the following output

Read 1 sets of 5001 points, dt = 0.2

std. dev.    relative deviation of
standard       ---------   cumulants from those of
set      average       deviation      sqrt(n-1)   a Gaussian distribition
cum. 3   cum. 4
SS1   7.234428e-01   1.087484e+02   1.537935e+00      -0.021    0.049

Data set 1 has strange time correlations:
the std. error using single points is larger than that of blocks of 2 points
The error estimate might be inaccurate, check the fit
a fitted parameter is negative
invalid fit:  e.e. 0.627815  a 1.14495  tau1 0.1214  tau2 0.843945
Will fix tau2 at the total time: 1000
Set   1:  err.est. 24.0042  a 0.975634  tau1 1.56619e-05  tau2 1000
******************************************************

Then I run g_energy to get Box_X and Box_Y values and I run the following:

g_analyze -f box_x.xvg  -av average.xvg -ee errest.xvg

Here is the output

****************G_ANALYZE BOX_X*******************
Read 1 sets of 5001 points, dt = 0.2

std. dev.    relative deviation of
standard       ---------   cumulants from those of
set      average       deviation      sqrt(n-1)   a Gaussian distribition
cum. 3   cum. 4
SS1   1.363121e+01   3.707014e-02   5.242510e-04       0.031   -0.354
a fitted parameter is negative
invalid fit:  e.e. -nan  a 0.0250074  tau1 0.501456  tau2 -960816
Will fix tau2 at the total time: 1000
a fitted parameter is negative
invalid fit:  e.e. 0.0665633  a -3.59838  tau1 829.806  tau2 1000
Will use a single exponential fit for set 1
Set   1:  err.est. 0.0969565  a 1  tau1 3421.07  tau2 0
******************************************************

How can I fix these errors? Could you give me any suggestion?