Functions for line intersections

8756e0b0-4786-49cc-b282-8d7a293f7675 111 Functions for line intersections Marco Bernacca 4 5 decimal

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These functions have been written to implement in Smath some features that are natively provided by either Scilab or Matlab in order to make available in Smath a function originally written in Matlab to find intersections between lines. The function in subject is P = InterX(L1, L2), written by NS. See below link: https://de.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections

Function mdiff(V) Input: a vector (either a row or a column) Output: a vector of the same nature of input (a row or a column) containing the differences V(i+1)-V(i). Number of output elements are lenght(V)-1.

Guess that the submatrix version must to be faster

Function mdiff(V)
Input: a vector (either a row or a column)
Output: a vector of the same nature of input (a row or a column)
                  containing the differences V(i+1)-V(i).
                   Number of output elements are lenght(V). V mdiff R V rows V rows 1 > (- V cols V cols 1 > (- matrix : ii 1 R length range R ii el V ii 1 + el V ii el - : for R 31 line :

V mdiff V rows 1 > V 0 stack 0 V stack - 2 V rows 11 submatrix V 0 augment 0 V augment - 112 V cols submatrix if eval :

z2 4273151 mat :

z2 mdiff 2 - 54 - 2 - 41 mat

z1 13589416 mat :

V 2 V length range el V 1 V length 1 - (range el -

Examples:

z1 mdiff 22315 - 15 mat

Function index(x; cond) Input: x: a vector (row or column). cond: expression evaluating to an array of T/F values. Output: a vector of same nature of input array whose components are those corresponding to a TRUE value for the given condition.

Index isn't used in this version of InterX

Function index(x; cond)
Input: x: a vector (row or column). cond: expression evaluating to an array of T/F values.
Output: a vector of same nature of input array whose components are those corresponding
                to a TRUE value for the given condition. V cond index j 0 : R 0 : c cond vectorize : 13 mat i 1 V length range c i el j j 1 + : R j el V i el : 21 line continue if for V rows 1 > R R transpose if eval 31 line :

Examples:

V rows 1 > V cond vectorize mwfind 2 el el V cond vectorize mwfind 2 el el transpose if eval

z1 z1 4 > index 58913 mat

z2 z1 mdiff 0 > index 427341 mat

Function plotG(x; y; char; size; color) Thanks to Omorr!! :-)

x y char size color plotG plot 05 matrix : i 1 x length range plot plot x i el y i el char size color augment stack : for plot 31 line :

Notice the use of matrix(0,5) as NULL.

xy char size color plotG xy cols 1 > xy 1 col xy 2 col char size color plotG xy Re xy Im char size color plotG if :

Function map(x; y; fun(2)) Input: x, y: vectors or matrices with compatible sizes. fun: a function of 2 argumens Output: vector or matrix whose elements are fun(el(x);el(y)) Apply a given function to corresponding elements of compatible arrays. For info on the Matlab concept of "arrays of compatible sizes" please refer to: https://it.mathworks.com/help/matlab/matlab_prog/compatible-array-sizes-for-basic-operations.html

Complete version, with error checking, but the other it's just a little faster.

x y 2 fun map xh x cols : xv x rows : yh y cols : yv y rows : 22 mat okx xh yh ≡ (xh 1 ≡ (yh 1 ≡ (| (| : oky xv yv ≡ (xv 1 ≡ (yv 1 ≡ (| (| : okx oky & X x : Y y : 12 mat xh yh < κ 2 yh range X X x augment : for 121 line xh yh > κ 2 xh range Y Y y augment : for 121 line 1 if if xv yv < κ 2 yv range X X x stack : for 121 line xv yv > κ 2 xv range Y Y y stack : for 121 line 1 if if 12 mat X Y fun vectorize 31 line Incompatible sizes error if 41 line :

xc x cols : xr x rows : yc y cols : yr y rows : 22 mat X x : Y y : 12 mat r xr yr Max : c xc yc Max : 12 mat X cols c < X X x augment : while Y cols c < Y Y y augment : while X rows r < X X x stack : while Y rows r < Y Y y stack : while X eval Y eval fun vectorize eval 81 line

x y 2 fun map xc x cols : xr x rows : yc y cols : yr y rows : 22 mat X x : Y y : 12 mat xc yc ≡ 0 xc yc < κ 2 yc range X X x augment eval : for κ 2 xc range Y Y y augment eval : for if if xr yr ≡ 0 xr yr < κ 2 yr range X X x stack eval : for κ 2 xr range Y Y y stack eval : for if if X Y fun vectorize eval 51 line :

a b plus a b + :

a b times a b * :

a b minus a b - :

a b divide a b / :

X Y fun vectorize r xr yr Max : c xc yc Max : 12 mat ρ 1 r range χ 1 c range Z ρ χ el X ρ χ el Y ρ χ el fun : for for 21 line ≡

Examples:

z1 z2 A B times map 4122032361626101618872135566328391524271213589456 mat

z2 z1 A B times map 4122032361626101618872135566328391524271213589456 mat

z2 z2 A B times map 164499151 mat

z1 z1 A B times map 192564811616 mat

z1 z1 A B plus map 26101618816 mat

z2 z2 A B plus map 84146251 mat

Function InterX(L1; L2) Input: L1; L2 : 2-rows matrices of coords (Row1 = x-coord; Row2 = y-coord) Output: 2-rows matricx of coords of intersecting points

L1 L2 InterX x1 L1 1 row transpose : x2 L2 1 row : y1 L1 2 row transpose : y2 L2 2 row : 14 mat dx1 x1 mdiff : dy1 y1 mdiff : dx2 x2 mdiff : dy2 y2 mdiff : 14 mat k 1 dx1 length range : S1 k el dx1 k el y1 k el * dy1 k el x1 k el * - : k 1 dx2 length range : S2 k el dx2 k el y2 k el * dy2 k el x2 k el * - : a b t a b A B times map : a b c d T a b t c d t - eval : x y D r x rows : c x cols : 12 mat X x 1 r 1 c 1 - submatrix y A B minus map : Y x 1 r 2 c submatrix y A B minus map : X Y t 41 line : C1 dx1 y2 dy1 x2 T S1 D : C2 y1 dx2 x1 dy2 T transpose S2 D : C1 C1 0 ≤ vectorize : C2 C2 0 ≤ vectorize transpose : 12 mat m n vals 13 mat C1 C2 & vectorize mwfind transpose eval : m m transpose : dx2 dx2 transpose : dy2 dy2 transpose : 13 mat L dy2 n el dx1 m el dy1 m el dx2 n el T : Lo L 0 ≠ vectorize mwfind 1 el eval : m m Lo el eval : n n Lo el eval : L L Lo el eval : 13 mat P1 dx2 n el S1 m el dx1 m el S2 n el T : P2 dy2 n el S1 m el dy1 m el S2 n el T : P1 P2 augment eval L L augment eval A B divide map eval 81 line 21 Zeros try 131 line :

Function D(x; y) Helper function for InterX. See below.

to 0 time :

Let's test it with a simple example:

L1 123456890112203 0.5 28 mat :

L2 34566579701332021429 mat :

tt L1 L2 InterX : 4.5 2 5.5 1 5.6667 0.6667 7.25 1.875 8.75 1.125 7.8333 2.75 8.5 1.75 72 mat

plot1 L1 L2 InterX o 12 Green plotG :

L1 transpose L2 transpose plot1 3 1 sys

and a bit more complicate one:

t 02 π * (2 π 100 / * range transpose :

r1 4 t * sin vectorize 2 + :

r2 8 t * sin vectorize 2 + :

c t cos vectorize :

s t sin vectorize :

xy1 r1 c * vectorize r1 s * vectorize stack :

xy2 r2 c * vectorize r2 s * vectorize stack :

XY xy1 xy2 InterX :

plot2 XY o 12 Green plotG :

xy1 transpose xy2 transpose plot2 3 1 sys

0 time to - 197.355 s *

In the hope that these brief notes could be of help to somebody, enjoy! Marco

Great! It works! So we have Smath performing like Scilab! Well, almost... The timing of Smath on my hardware says:

Whilst, on same hardware, Scilab says:

and this is expressed in seconds... But anyway Smath is a great tool!!