THE 'INPUT MTZ DATA' OPTION

INTRODUCTION

The 'Input MTZ Data' option enables the input of data from one or more MTZ files to be read into the program so that it may be included in the analyses of data coverage. Data may be read from unmerged (multirecord) or merged MTZ data files. Note that any currrently stored MTZ data will be cleared if a new parameters file is read in or the program defaults are reset.

List of sections:

Inputting the Data
Using the MTZ Data in Analyses
Resolution for Data Analyses

INPUTTING THE DATA

When the 'Input MTZ Data' option is selected, the following menu is displayed:

   <Multirecord MTZ File>
   <Standard with Anomalous>
   <Standard - No Anomalous>
   <Clear MTZ Data>

   <Return to Main Menu>

The first three menu items enable the selection of the required format for the input MTZ file. The fourth option clears any currently stored MTZ data. When one of the file input items is selected, the following prompt is output:

File name (default ext=.mtz):

The user replies with the name of the required MTZ reflection data file; if no file extension is given, an extension of .mtz is assumed. A blank reply will cancel the request. The program checks that the file exists and can be opened; if there is an error, an error message will be output and the prompt will be repeated.

If MTZ data are already stored in the program, the following prompt will be output:

Overwrite current MTZ data (y/n) [y]:

The user replies with 'y' (the default) to overwrite the existing stored MTZ data with the data to be read in or 'n' if such data is not to be overwritten; in the latter case the following prompt will then be output:

Add to current MTZ data (y/n) [y]:

If the user replies with 'y' (the default) the new MTZ data will be added to the currently stored MTZ data. If the user replies with 'n' then the MTZ input option will be abandoned.

If a multirecord file is being read then it is assumed to have the standard columns of H K L M/ISYM I present. For a standard merged MTZ file, the user is first given the option of listing the column labels (up to the first 20) from the input file in response to the following prompt:

Show labels (max. of 20) in MTZ file (y/n) [n]:

Again for a standard MTZ file, the program will prompt for two or four column labels showing the program labels of the required columns:

Label for F [F]:
Label for sig(F) [SIGF]:

and, if anomalous data are present

Label for delta_anom [DANO]:
Label for sig(delta_anom) [SIGDANO]:

An error notice will be output if all the required columns are not found and the file input will be abandoned. Otherwise the data will be read from the MTZ file and stored within the program. The number of MTZ reflections read and the total now stored will be logged. For a standard MTZ file with anomalous data, the number of MTZ reflections which form an anomalouus pair (anomalous difference defined) will also be logged; each such pair will add two reflections to the stored total. If the MTZ file is successfully read, the program will return to the main menu.

USING THE MTZ DATA IN ANALYSES

The following points should be noted when interpreting results from the analyses which include MTZ data.

All MTZ reflections are considered to be of unknown partality and are, in effect, treated as fully recorded reflections.
All MTZ reflections are treated as being non-spatially overlapped.
Reflections from standard MTZ files will be of unknown sign if the MTZ file does not include anomalous data or if their anomalous differences are missing. Such reflections of unknown sign are necessarily excluded from any analyses of acentric pairs.
Reflections from a standard MTZ file will be included with a multiplicity of one or, if anomalous pairs are present, two. This must be borne in mind when looking at any multiplicity analyses which may thus not be a true reflection of actual situation.

RESOLUTION FOR DATA ANALYSES

When MTZ data are read, the resolution of the data will also be determined from the MTZ file. When carrying out analyses of MTZ data alone, the user has the option of using the resolution from the MTZ file rather than the resolution defined in the parameter table for the first crystal set. If several sets of MTZ are currently stored, then the resolution from the first of these sets input is the value offered.