11.5. FIDO Input System

L. M. Petrie


This document provides a description of the FIDO input system being used in conjunction with several SCALE functional modules. The FIDO system is a widely used method of entering or modifying large data arrays with minimum effort. Special advantage is taken of patterns of repetition or symmetry whenever possible.


This document was funded by the Office of Nuclear Material Safety and Safeguards, U.S. Nuclear Regulatory Commission, for inclusion within the SCALE manual.

11.5.1. Introduction

The FIDO input method is specially devised to allow entering or modifying large data arrays with minimum effort. Advantage is taken of patterns of repetition or symmetry wherever possible. The FIDO system was patterned after the input method used with the FLOCO coding system at Los Alamos and was first applied to the DTF-II code. Since that time, numerous features requested by users have been added, a free-field option has been developed, and the application of FIDO has spread to innumerable codes. Starting with SCALE 5, the FIDO routines have been converted to Fortran 90, and the requirement that arrays be held in a large container array has been removed.

The data are entered in units called “arrays.” An array comprises a group of contiguous storage locations that are to be filled with data at the same time. These arrays usually correspond on a one-to-one basis with Fortran arrays used in the program. A group of one or more arrays read with a single call to the FIDO package forms a “block,” and a special delimiter is required to signify the end of each block. Arrays within a block may be read in any order with respect to each other, but an array belonging to one block must not be shifted to another. The same array can be entered repeatedly within the same block. For example, an array could be filled with “0” using a special option, and then a few scattered locations could be changed by reading in a new set of data for that array. If no entries to the arrays in a block are required, the delimiter alone satisfies the input requirement.

Three major types of input are available: fixed-field input, free-field input, and user-field input.

11.5.2. Fixed-Field Input

The fixed-field input option is documented here for completeness.


The use of fixed-field input is NOT recommended. Use the free-field input option documented in Sect. 11.5.3.

Each record is divided into six 12-column data fields, each of which is divided into three subfields. The following sketch illustrates a typical data field. The three subfields always comprise 2, 1, and 9 columns, respectively.


To begin the first array of a block, an array originator field is placed in any field on a record:

Subfield 1: An integer array identifier < 100 specifying the data array to be read in.

Subfield 2: An array-type indicator:

“$” if the array is integer data

“*” if the array is real data

“#” if the array is double-precision data

Subfield 3: Blank

Data are then placed in successive fields until the required number of entries has been accounted for.

In entering data, it is convenient to think of an “index” or “pointer” as a designator that is under the control of the user and which specifies the position in the array into which the next data entry is to go. The pointer is always positioned at array location #1 by entering the array originator field. The pointer subsequently moves according to the data operator chosen. Blank fields are a special case in that they do not cause any data modification and do not move the pointer.

A data field has the following form:

Subfield 1: The data numerator, an integer <100. We refer to this entry as N1 in the following discussion.

Subfield 2: One of the special data operators listed below.

Subfield 3: A nine-character data entry, to be read in F9.0 format. It will be converted to an integer if the array is a “$” array or if a special array operator such as Q is being used. Note that an exponent is permissible but not required. Likewise, a decimal is permissible but not required. If no decimal is supplied, it is assumed to be immediately to the left of the exponent, if any; and otherwise to the right of the last column. This entry is referred to as N3 in the following discussion.

A list of data operators and their effect on the array being input follows:


indicates a single entry of data. The data entry in the third subfield is entered in the location indicated by the pointer, and the pointer is advanced by one. However, an entirely blank field is ignored.

“+” or “-“

indicates exponentiation. The data entry in the third field is entered and multiplied by \(10^{\pm N_{1}}\) where N1 is the data numerator in the first subfield, given the sign indicated by the data operator itself. The pointer advances by one. In cases where an exponent is needed, this option allows the entering of more significant figures than the blank option.


has the same effect as “+.”


indicates that the data entry is to be repeated N1 times. The pointer advances by N1. The entry 5R1 is equivalent to 1 1 1 1 1.


indicates linear interpolation. The data numerator, N1, indicates the number of interpolated points to be supplied. The data entry in the third subfield N3 is entered, followed by Nj interpolated entries equally spaced between that value and the data entry found in the third subfield of the next nonblank field. The pointer is advanced by N1 + 1. The field following an “I” field is than processed normally, according to its own data operator. The “I” entry is especially valuable for specifying a spatial mesh. For example, the entry 3I 10 50 is equivalent to 10 20 30 40 50. In “$” arrays, interpolated values will be rounded to the nearest integer.


indicates logarithmic interpolation. The effect is the same as that of “I” except that the resulting data are evenly separated in log-space. This feature is especially convenient for specifying an energy mesh. For example, the entry 3L 1 1+4 is equivalent to 1 10 100 1000 10000.


is used to repeat sequences of numbers. The length of the sequence is given by the third subfield, N3. The sequence of N3 entries is to be repeated N1 times. The pointer advances by N1*N3. If either N1 or N3 is 0, then a sequence of N1 + N3 is repeated one time only, and the pointer advances by N1 + N3. This feature is especially valuable for geometry specification.

The “N” option

has the same effect as “Q,” except that the order of the sequence is reversed each time it is entered. This feature is valuable for the type of symmetry possessed by Sn quadrature coefficients.


has the same effect as “N,” except that the sign of each entry in the sequence is reversed each time the sequence is entered. For example, the entries

1 2 3 2M2

would be equivalent to

1 2 3 -3 -2 2 3.

This option is also useful in entering discrete ordinates angular quadrature coefficients.


causes N1 + N3 locations to be set at 0. The pointer is advanced by N1 + N3.


causes the position of the last array entered to be printed. This is the position of the pointer, less 1. The pointer is not moved.


causes the print trigger to be changed. The trigger is originally off. Successive “O” fields turn it on and off alternately. When the trigger is on, each record is listed as it is read.


indicates that the pointer is to skip N1 positions leaving those array positions unchanged. If the third subfield is blank, the pointer is advanced by N1. If the third subfield is nonblank, that data entry is entered following the skip, and the pointer is advanced by N1 + 1.


moves the pointer to the position, N3 specified in the third subfield.


fills the remainder of the array with the datum entered in the third subfield. For example, F9 will fill all positions of the array with a value of 9.


skips over the remainder of the array. The array length criterion is always satisfied by an E, no matter how many entries have been specified. No more entries to an array may be given following an “E,” except that data entry may be restarted with an “A.”

The reading of data to an array is terminated when a new array origin field is supplied, or when the block is terminated. If an incorrect number of positions has been filled, an error edit is given; and a flag is set which will later abort execution of the problem. FIDO then continues with the next array if an array origin was read. Otherwise, control is returned to the calling program.

A block termination consists of a field having “T” in the second subfield. Entries following “T” on a record are ignored, and control is returned from FIDO to the calling program.

Comment records can be entered within a block by placing an apostrophe (‘) in column 1. Then columns 2–80 will be listed, with column 2 being used for printer carriage control. Such records have no effect on the data array or pointer.

11.5.3. Free-Field Input

With free-field input, data are written without fixed restrictions as to field and subfield size and positioning on the record. The options used with fixed-field input are available, although some are slightly restricted in form. In general, fewer data records are required for a problem, the interpreting print is easier to read, a record listing is more intelligible, the records are easier to enter, and certain common data entry errors are tolerated without affecting the problem. Data arrays using fixed- and free-field input can be intermingled at will within a given block.

The concept of three subfields per field is still applicable to free-field input; but if no entry for a field is required, no space for it need be left. Only columns 1–72 may be used, as with fixed-field input. A field may not be split across records.

The array originator field can begin in any position. The array identifiers and type indicators are used as in fixed-field input. The type indicator is entered twice to designate free-field input (i.e., “$$,” “**,” or “##”). The blank third subfield required in fixed-field input is not required. For example,


indicates that array 31, a real-data array, will follow in free-field format.

Data fields may follow the array origin field immediately. The data field entries are identical to the fixed-field entries with the following restrictions:

1. Any number of blanks may separate fields, but at least one blank must follow a third subfield entry if one is used.

2. If both first- and second-subfield entries are used, no blanks may separate them (i.e., 24S, but not 24 S).

3. Numbers written with exponents must not have imbedded blanks (i.e., 1.0E+4, 1.0-E4, 1.0+4, or even 1+4, but not 1.0 E4). A zero should never be entered with an exponent. For example, 0.00 - 5 or 0.00E - 5 will be interpreted as - 5 \(\times\) 10-2.

4. In third-subfield data entries only 9 digits, including the decimal but not including the exponent field, can be used (i.e., 123456.89E07, but not 123456.789E07).

  1. The Z entry must be of the form: 738Z, not Z738 or 738 Z.

  2. The + or - data operators are not needed and are not available.

7. The Q, N, and M entries are restricted: 3Q4, 1N4, M4, but not 4Q, 4N, or 4M.

11.5.4. User-Field Input

If the user follows the array identifier in the array originator field with the character “U” or “V,” the input format is to be specified by the user. If “U” is specified, the FORTRAN FORMAT to be used must be supplied in columns 1–72 of the next record. The format must be enclosed by the usual parentheses. Then the data for the entire array must follow on successive records. The rules of ordinary FORTRAN input as to exponents, blanks, etc., apply. If the array data do not fill the last record, the remainder must be left blank.

“V” has the same effect as “U,” except that the format read in the last preceding “U” array is used.

11.5.5. Character Input

If the user wishes to enter character data into an array, at least three options are available. The user may specify an arbitrary format using a “U” and reading in the format. The user may follow the array identifier by a “/.” The next two entries into subfield 3 specify the beginning and ending indices in the array into which data will be read. The character data are then read starting with the next data record in an 18A4 format if going to a real or integer array, and 9AB if going to a double precision array.

Finally, the user may specify the array as a free-form “*” array and then specify the data entries as “nH” character data where n specifies how many characters follow H.