## IOBasic

Date

Abstract

Thorn IOBasic provides I/O methods for outputting scalar values in ASCII format into ﬁles and for printing them as runtime information to screen.

### 1 Purpose

Thorn IOBasic registers 2 I/O methods with the I/O interface in the ﬂesh which both output the same following information:

• for CCTK_SCALAR variables, the value of the scalar versus time
• for CCTK_GF and CCTK_ARRAY variables, the values of global reduction operations (eg. minimum, maximum, L1, and L2 norm) versus time

The I/O methods diﬀer in the destination the output is written to:

• Scalar
This method outputs the information into ASCII ﬁles named "<scalar_name>.{asc|xg}" (for CCTK_SCALAR variables) and "<var_name>_<reduction>.{asc|xg}" (for CCTK_GF and CCTK_ARRAY variables where reduction would stand for the type of reduction value that is output).
The output data can be plotted by using either xgraph (for "*.xg" ﬁles) or gnuplot (for "*.asc" ﬁles). The output style can be selected via parameter settings.
• Info
This method prints the data as runtime information to stdout.
The output occurs as a table with columns containing the current iteration number, the physical time at this iteration, and more columns for scalar/reduction values of each variable to be output.

### 2 IOBasic Parameters

Parameters to control the Scalar I/O method are:

• IOBasic::outScalar_criterion (steerable)
The criterion that decides when to Scalar output. If this parameter is set in the parameter ﬁle, it will override the setting of the shared IO::out_criterion parameter.
• IOBasic::outScalar_every (steerable)
How often, in terms of iterations, to do Scalar output. If this parameter is set in the parameter ﬁle, it will override the setting of the shared IO::out_every parameter.
• IOBasic::outScalar_dt (steerable)
How often, in terms of simulation time, to do Scalar output. If this parameter is set in the parameter ﬁle, it will override the setting of the shared IO::out_dt parameter.
• IOBasic::out_dir
The directory in which to place the Scalar ASCII output ﬁles. If the directory doesn’t exist at startup it will be created.
If this paraeter is set to an empty string Scalar output will go to the standard output directory as speciﬁed in IO::out_dir.
• IOBasic::outScalar_style
How to start comments in the Scalar ASCII output ﬁles.
Possible choices for this keywork parameter are xgraph and gnuplot.
• IOBasic::out_format (steerable)
The output format for ﬂoating-point numbers in Scalar output.
This parameter conforms to the format modiﬁer of the C library routine fprintf(3). You can set the format for outputting ﬂoating-point numbers (ﬁxed or exponential) as well as their precision (number of digits).
• IOBasic::outScalar_vars (steerable)
The list of variables to output into individual ASCII ﬁles.
The variables must be given by their fully qualiﬁed variable or group name. The special keyword all requests Scalar output for all variables. Multiple variables must be separated by spaces. For CCTK_GF and CCTK_ARRAY variables, an option string can be appended in curly braces to the name of the variable. The only option supported so far is an individual list of reductions for that variable which would take precedence over the default reduction operations to perform.
• IOBasic::outScalar_reductions (steerable)
The list of global reduction operations to perform on CCTK_GF and CCTK_ARRAY variables for Scalar output. This setting can be overridden for individual variables using an option string.
Multiple reduction names must be separated by spaces.

Parameters to control the Info I/O method are:

• IOBasic::outInfo_criterion (steerable)
The criterion that decides when to Info output. If this parameter is set in the parameter ﬁle, it will override the setting of the shared IO::out_criterion parameter.
• IOBasic::outInfo_every (steerable)
How often, in terms of iterations, to do Info output. If this parameter is set in the parameter ﬁle, it will override the setting of the shared IO::out_every parameter.
• IOBasic::outInfo_dt (steerable)
How often, in terms of simulation time, to do Info output. If this parameter is set in the parameter ﬁle, it will override the setting of the shared IO::out_dt parameter.
• IOBasic::outInfo_vars (steerable)
The list of variables to output to screen.
The variables must be given by their fully qualiﬁed variable or group name. The special keyword all requests Info output for all variables. Multiple variables must be separated by spaces.
For CCTK_GF and CCTK_ARRAY variables, an option string can be appended in curly braces to the name of the variable. The only option supported so far is an individual list of reductions for that variable which would take precedence over the default reduction operations to perform.
• IOBasic::outInfo_reductions (steerable)
The default list of global reduction operations to perform on CCTK_GF and CCTK_ARRAY variables. This setting can be overridden for individual variables using an option string.
Multiple reduction names must be separated by spaces.

All of the above parameters marked as steerable can be changed at runtime.

### 3 Examples

#### 3.1 Example for Info Output

The following parameter settings request info output for variables grid::r, wavetoy::phi (both are CCTK grid functions) and mythorn::complex (a complex CCTK scalar) at every other iteration.

The minimum and maximum of grid::r is printed according to the list of default reductions for info output (parameter IOBasic::outInfo_reductions). This list is overridden for wavetoy::phi where only the L2 norm is output as speciﬁed in the option string for this variable. You can also add other reduction operators within the $\left\{\right\}$ braces.

For the scalar variable mythorn::complex both the real and imaginary part are printed.

IOBasic::outInfo_every      = 2
IOBasic::outInfo_vars       = "grid::r
wavetoy::phi{reductions = ’norm2’}
mythorn::complex"
IOBasic::outInfo_reductions = "minimum maximum"

The resulting screen output would look like this:

---------------------------------------------------------------------------------------------
it  |          | GRID::r                     | WAVETOY::phi | MYTHORN::complex            |
|    t     | minimum      | maximum      | norm2        | real part    | imag part    |
---------------------------------------------------------------------------------------------
0 |    0.000 |   0.02986294 |   0.86602540 |   0.04217014 |   6.90359593 |   0.00000000 |
2 |    0.034 |   0.02986294 |   0.86602540 |   0.00934749 |   6.90359593 |   0.00000000 |
4 |    0.069 |   0.02986294 |   0.86602540 |   0.02989811 |   6.90359593 |   0.00000000 |
6 |    0.103 |   0.02986294 |   0.86602540 |   0.05899959 |   6.90359593 |   0.00000000 |
8 |    0.138 |   0.02986294 |   0.86602540 |   0.07351147 |   6.90359593 |   0.00000000 |
10 |    0.172 |   0.02986294 |   0.86602540 |   0.07781795 |   6.90359593 |   0.00000000 |

#### 3.2 Example for Scalar Output

The following parameter settings request scalar output for all grid function variables in the group grid::coordinates and for the scalar variable grid::coarse_dx.
Output occurs every 10th iteration. gnuplot output style is selected for the ASCII ﬁles which are placed into a subdirectory scalar_output. The minimum and maximum of grid::r is printed according to the list of default reductions for scalar output (parameter IOBasic::outScalar_reductions). This list is overridden for wavetoy::phi where only the L1 norm is output as speciﬁed in the option string for this variable. You can also add other reduction operators within the $\left\{\right\}$ braces.

IOBasic::outScalar_every      = 10
IOBasic::outScalar_vars       = "grid::coordinates grid::coarse_dx wavetoy::phi{reductions = ’norm1’}"
IOBasic::outScalar_reductions = "minimum maximum"
IOBasic::outScalar_style      = "gnuplot"
IOBasic::out_dir              = "scalar_output"

This would create the following ASCII ﬁles: