Simimary of Subroutine ; 



If MAX equals three or more when MOVE is called, FKBAE for the previous MAX 

 is used in obtaining approximations of XX, YY, and M. (For MAX = 2., FKBAE 

 is set equal to FK. ) SUEFCE is called and returns FKK for this approximation 

 at XX, YY. FKBAR is then redefined as (FK+FKX)/2. If the difference between 

 FKEAH and FKKP is less than O..OOOO9/D, the current XX, YY, AA, and FKK values 

 are accepted for the new point. If the difference is greater, FKKP is set 

 equal to FKBAH, and the current FKEAJR is used to obtain another set of XX, 

 YY, AA, and FKK values. The difference between FKBAR and FKKP is again 

 tested. This cycle may repeat a maximum of 20 times before termination. If 

 the cycle stops before IT = 20, MIT is set equal to one. If the cycle stops- 

 at IT = 20, and if the difference between FKBAR and fkkPP is less than 

 0.00009/D, then MIT is set equal to two, and FKBAR is defined as CFKBAR+FKKP)/2 

 for obtaining XX, YY, AAA, and FKK. If IT = 20, and this difference is 

 greater than O.OOOO9/D, then MIT is set equal to three. When MIT = 3, 

 control is transferred back to RAYTJ immediately. When MIT = 1 or 2, XX and 

 YY are tested to see if the new point has reached the €d.ge of the grid. 

 WGO = 2 if the ray has reached the edge of the grid, and NGO = 1 if it has 

 not. 



Remarks : 



MIT - 1 when the curvatiire approximations are converging to a single vaiue. 

 MIT = 2 when the approximations are oscillating between two values. In this 

 case the average of the two values is taken as the new curvature. MIT = 3 

 when the approximations are oscillating among three or more values. Wo 

 valid curvature approximation can be made in this case ; this is one basis for 

 the terminiation of a ray. 

 The use of Sense Switch 2 allows the operator to observe successive IT and 



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