Two Stage Sorting System Using Two-line Sorting Switches

Abstract

A partial sorting system utilizing two-line sorting switches for applications where the order of numbers changes slowly with respect to sorting frequency. By using only two stages of sorting and making sorting passes at a relatively high frequency, large reductions in required hardware are obtained while still having a completely sorted output during the major portion of normal system operation.

Description

This invention relates to electronic data processing and more particularly to apparatus which may be used to sort randomly arranged information.

In many applications it s desirable to sort randomly arranged data into a predetermined order. Systems which may be used for this type of sorting are disclosed in U.S. Pat. Nos. 3,029,413 and 3,311,892, granted to the same inventor and assigned to the predecessor of the same assignee as the present invention. The invention disclosed therein are concerned primarily with a complete sort of data. However, in some applications a partial sort may be all that is necessary. For example, if the data to be sorted is a table of target ranges to be displayed on a radar scope, then, since the relative target positions will generally change slowly, relative to the frequency of sorting, a partial sort will be satisfactory. Furthermore, by repeating the operation supplying the data back to the first stage in the order in which it is sorted by the second stage, a complete sort is accomplished in what will be an acceptably short time for many applications. The present application discloses how a plurality of sorting switches such as those described in U.S. Pat. No. 3,311,892 may be arranged to perform a partial sort, thereby reducing the amount of hardware required and reducing delays in the sorting process.

It is the object of this invention to provide a partial sorting system useful in sorting the type of data where the relative magnitudes of the data items is not likely to change rapidly relative to the frequency at which it is practical to sort.

Another object is to provide a sorting system where a complete sort of data items, none of which is more than two places out of order, may be accomplished.

It is also an object of this invention to provide a sorting system where a complete sort of data items may be accomplished by successive passes through the system.

A further object is to provide a sorting system useful to sort range data to be displayed on a radar display.

Other objects will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to the others, and the apparatus embodying features of construction, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a block diagram of a radar display system with simulated targets in which the invention may be used;

FIG. 2 a is a tabulation of the order of data items at the inputs and outputs of the switches of FIG. 2 b for three successive passes through the switches;

FIG. 2 b is a block diagram of the preferred arrangement of two line sorting switches to sort four data items; and

FIG. 3 is a block diagram of the preferred arrangement of two line sorting switches to sort six data items.

FIG. 1 shows a system in which the present invention may be used. This is a system for simulating targets on a radar scope. Target information is supplied to a computer 10 where it is stored and a range to the targets computed. At startup, values representing the target ranges are output in random order to the sorter 12, the sorting system of the invention, where they are arranged in order or decreasing range, in a manner explained hereinafter. From sorter 12 the sorted target ranges are sequentially input to comparator 14 by sequencer 16. In comparator 14 they are compared with the output of counter 18 which provides a value representing the instantaneous range of the sweep on the radar scope 20. (It is assumed scope 20 is of the spiral scan type.) When a comparison occurs, an output to the video channel of radar scope 20 occurs and a blip will appear on the scope. The output from sorter 12 is also fed back to the computer indicating the order for the inputs to sorter 12 on the next pass, as will be explained below.

FIG. 2 b is a block diagram of sorter 12 containing three two-line sorting switches 22 of the type described in U.S. Pat. No. 3,311,892. Although only three switches (arranged to accept four initial inputs) are shown, the system may be expanded to accept as many inputs as necessary. As is explained in the above patent, each switch will always have on a specified output line the higher of its two inputs regardless of the input line on which the higher value appears.

Examination of the tables of FIG. 2 a along with FIG. 2 b will help explain the sorting operation. Assume that four stored ranges, A,B,C, and D are supplied from computer 10 in increasing order (i.e., A is low, B is 3 rd high, C 2 nd high and D high) as the inputs i1 through i4 to sorter 12. The desired output would be D,C,B,A in descending order. Table 1 of FIG. 2a shows how these values will migrate through the sorter. A (on input i.sub.1) is lower than B (on i.sub.2, whereby, through operation of switch 22, A will appear on m.sub.2 and B on m.sub.1. In a like manner, D will appear on m.sub.3 and C on m.sub.4, by operation of switch 22'. In switch 22" A and D will be reversed with a final output of B on o.sub.1, D on o.sub.2, A on o.sub.3 and C on o.sub.4. This is not the desired result of a complete sort into descending order. HOwever, this order of BDAC is fed back to the computer and on the next pass the values will be input to sorter 12 in this new order. An examination of Table 2 reveals that this time the proper order will result. Thus, in two passes, a complete sort will result. The first output then will have been in error as will any output where, for example, A, the lowest and D the highest must change places. However, this is very unlikely in applications such as target range sorting because of the nature of relative motion and when it does occur, it causes a wrong output for only one iteration and will appear to be interference rather than a false reading on the scope.

Table 3 of FIG. 2 a shows what happens if two adjacent targets change relative position, the type of change normally expected. Suppose A has become larger than B. i.e. A is moving away and/or B is coming closer. Although the feedback from sorter 12 instructs a computer output in the D, C, B, A sequence the value of A and/or B will be appropriately changed by normal computer operation. As shown, the order at the output from the first stage will now be D, C, A, B. The output from the second stage remains the same since the values are in the proper order. If the value of A changes by a large enough factor to be greater than both B and C, the fully sorted order of D, A, C, B would be output from the second stage.

FIG. 3 shows a six-line partial sorting system with the individual switches arranged in first and second stages according to the present invention. Similar analysis of the switching in this system shows that if the highest number is in the lowest position it will take two incorrect passes before the number migrates to its proper position. This could probably only occur on start up. In any other case it is very unlikely that an item could get that far out of place. It should also be noted that it is a normal practice to output the ranges from the computer five times a second. Thus, in the above case, incorrect data would be present at the radar scope for only two-fifths of a second.

For applications of this nature, where large changes are not expected in the relative magnitude of the data items being sorted in relation to the sorting frequency, a large saving in hardware and time results with the present invention. For example, a complete sort using the system described in U.S. Pat. No. 3,029,413 (FIG. 3 and FIG. 4) for four input lines requires five or six sorting switches as compared to three in the present invention. A six-line sorting system using the prior system requires twelve switches whereas the present invention requires only five switches.

The embodiments of sorters disclosed in FIGS. 2 b and 3 both are arranged to receive an even number of initial inputs, whereby a number of first stage switches equal to half the number of inputs, and a number of second stage switches equal to one less than the number of first stage switches, are provided. If the number of inputs to be sorted is an odd number, the last input would be supplied directly to a second stage switch, the latter then being equal in number to the first stage switches. In FIG. 2 b, for example, if only three inputs were to be sorted input i.sub.3 would be supplied directly to switch 22" in place of m.sub.3 and switch 22' would be omitted. Thus, only one first and one second stage switch are required to sort three inputs.

Claims

What is claimed is:

1. A method of partially sorting N binary coded numbers, where N is greater than four, into a descending order of precedence said method comprising, when N is even:

a. providing the N numbers in pairs as respective simultaneous inputs to a first row made up of M two-line sorting switches where M equals N/2, each switch having a high and a low output; and

b. providing N- 2 of said first-row outputs to a second row of M-1 two-line sorting switches, the high output of the first switch and the low output of the last switch in said first row not being connected to a second row switch, and all of the remaining first row high and low outputs being connected so that, with said first switch in each row considered as the highest order switch and the last switch as the lowest order switch, a low output from any higher order switch and a high output from the next lower order switch in said first row are connected to the switch in said second row having the same order as that of said higher order switch in said first row; and when N is odd, said method comprising; comprising;

c. providing N- 1 of said N numbers in pairs as respective simultaneous inputs to a first row made up of M of said two-line sorting switches where M =N-1;/2

d. providing N-2 of said first row outputs to a second row of M two-line sorting switches, the high output of the first switch in said first row not being connected to a second row switch, the low output of the last switch in said first row being connected as one input to the last switch in said second row, and all the remaining first row outputs being connected in the same manner as the remaining first row outputs for N even; and

e. providing the remaining one of the N inputs not provided as an input to said first row as the second input to said last switch in said second row,

whereby said high output of said first switch in said first row may be designated as having the highest order of precedence, the high output of the first switch in the second row the next highest, the low output of said first switch in the second row the next highest, the low output of said first switch in the second row the next highest, the high and low outputs of any remaining switches providing in like manner successively lower orders of precedence, the lowest being the low output of the last switch in said first row for N even and the low output of the last switch in said second row for N odd.

2. The invention according to claim 1 wherein said coded numbers are provided to said sorting switches in a partially sorted descending order with none of said numbers more than two places out of the position it would have in a true descending order with the number in the highest order position being provided to a first input of the first switch in said first row, the next highest the second input to said first switch, the next highest a first input to the second switch in said first row and so on, the input in the lowest order position being provided to the second input of the last switch in said first row for N even and to the second input of the last switch in said second row for N odd, whereby in a single pass through said first and second rows a complete sort of said numbers into descending order will occur.

3. The invention according to claim 1 and further including the step of successively passing said N numbers through said sorting switches the input order of said numbers being the output order on the last pass with the number designated as being the highest order of precedence as a first input to the first switch in said first row, the next highest the second input to said first switch, the next highest a first input to the second switch in said first row and so on, the lowest order being provided to the second input of last switch in said first row for N even and to the second input of the last switch in said second row for N odd, whereby in not more than N/2 passes for N even and (N + 2)/2 passes for N odd, a complete sort will be accomplished irrespective of the initial arrangement of said numbers.

4. The method according to claim 3 wherein said binary coded numbers are outputs from a digital computer and the sorted outputs obtained on one pass are fed back to said computer to establish the output order on the next pass.

5. The method according to claim 4, wherein said binary coded numbers represent radar ranges to targets computed in a digital computer and the sorted outputs are provided as inputs to a radar display system.

6. The method according to claim 5 wherein the rate of successive passes is 5 times per second or greater, whereby any incorrect output order will exist for only a short period of time and such error will appear as interference on said radar display system.

7. Apparatus for partially sorting N binary coded numbers, where N is greater than four, into a descending order of precedence, said apparatus comprising when N is even:

a. a first row made up of M two-line sorting switches where M equals N/2, each switch having a high and a low output and having said N numbers as inputs; and

b. a second row of M-1 two-line sorting switches having N-2 of the first row outputs as inputs, the high output of the first switch and the low output of the last switch in said first row not being connected to a second row switch, and all of the remaining first row high and low outputs being connected so that, with said first switch in each row considered as the highest order switch and the last switch the lowest order switch, a low output from any higher order switch and a high output from the next lower order switch in said first row are connected to the switch in the second row having the same order as that of said higher order switch in said first row; and said apparatus comprising, when N is odd:

c. a first row made up of M of said two-line sorting switches where M = (N-1)/2 and having N-1 of said N numbers as inputs;

d. a second row of M two-line sorting switches having N-2 of the first row outputs as inputs, the high output of the first switch in said first row not being connected to a second row switch, the low output of the last switch in said first row being connected as one input and the remaining one of the N numbers which is not an input to said first row as the other input to the last switch in said second row, and all the remaining first-row outputs being connected in the same manner as the remaining first row outputs for N even,

whereby said high output of said first switch in said first row may be designated as having the highest order of precedence, the high output of the first switch in the second row the next highest, the low output of said first switch in the second row the next highest, the high and low outputs of any remaining switches, providing in like manner successively lower orders of precedence, the lowest being the low output of the last switch in said first row for N even and the low output of the last switch in said second row for N odd.

8. The invention according to claim 7 and further including means to provide said coded numbers to said sorting switches in a partially sorted descending order with none of said numbers more than two places out of the position it would have in a true descending order with the number in the highest order position being provided to a one input of the first switch in said first row, the next highest to the other input of said first switch, the next highest to one input of the second switch in said first row and so on, the input in the lowest order position being provided as an input to the last switch in said first row for N even and as an input to the last switch in said second row for N odd, whereby in a single pass through said first and second rows a complete sort of said numbers into descending order will occur.

9. The invention according to claim 7 and further including means for successively passing said N numbers through said sorting switches the input order of said numbers being the output order on the last pass with the number designated as being the highest order of precedence as a one input to the first switch in said first row, the next highest the other input to said first switch, the next highest one input to the second switch in said first row and so on, the lowest order being provided as an input to the last switch in said first row for N even and as an input to the last switch in said second row for N odd, whereby in not more than N/2 passes for N even and (N+2)/2 passes for N odd, a complete sort will be accomplished irrespective of the initial arrangement of said numbers.

10. Apparatus according to claim 9 wherein said means comprises a digital computer.

11. Apparatus according to claim 10 wherein said binary coded numbers represent radar ranges to a target computed and stored in said computer and further including radar display means connected to said sorted outputs.