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For Tim,
Here's a very simple x,y scatterplot and trendline based on my previous trendline code.
'
Here's a very simple x,y scatterplot and trendline based on my previous trendline code.
'
Code:
#COMPILE EXE
#DEBUG ERROR ON
#DEBUG DISPLAY ON
#DIM ALL
#INCLUDE ONCE "WIN32API.INC"
FUNCTION PBMAIN () AS LONG
LOCAL n, i AS LONG
LOCAL slope, offset AS EXT
LOCAL xMin,xMax AS EXT
LOCAL yMin,yMax,ypmax AS EXT
LOCAL hGraph AS DWORD
LOCAL strGType AS STRING
'Build a data set
n = 99 ' 100 points -1 because we are using a zero based array
xMin = 0: xMax = 100 ' range to plot on x Axis.
DIM dp(n,1) AS EXT ' x values in dp(i,0), y values in dp(i,1)
RANDOMIZE TIMER
'Comment out one of the two following plot types
'scatter plot
strGType = "Scatter Plot"
FOR i = 0 TO n
dp(i,0) = RND(1,100)
dp(i,1) = RND(1,100)
IF dp(i,1) > ypmax THEN ypmax = dp(i,1)
NEXT
'linear plot
' strGType = "Linear Plot"
' FOR i = 0 TO n
' dp(i,0) = i
' dp(i,1) = RND(1,20) + i * RND(1,5) ' slowly increment average y
' IF dp(i,1) > ypmax THEN ypmax = dp(i,1)
' NEXT
'Get linear trendline formula
Trendline dp(),slope,offset
yMin = offset: yMax = slope * xMax + offset
? "Trendline is: y = " & FORMAT$(slope,"0.00") & IIF$(offset >= 0,"x +","x ") & FORMAT$(offset,"0.00") & $CRLF _
& USING$("Line from (#.# , #.# ) to (#.# , #.#)",xMin,yMin,xMax,yMax)
'===== DRAW GRAPH ===================
GRAPHIC WINDOW NEW strGType,100,100,600,600 TO hGraph
'scale window
GRAPHIC SCALE (-10,ypMax+10) - (xMax+10,-10) 'invert co-ordinate system and put border around graph
'draw axes
GRAPHIC LINE (0,0) - (0,ypmax)
GRAPHIC LINE (0,0) - (xMax,0)
'Plot points
FOR i = 0 TO n
GRAPHIC SET POS (dp(i,0),dp(i,1))
GRAPHIC PRINT "x"
'graphic line (dp(i,0),0)- (dp(i,0),dp(i,1)),%BLACK
NEXT
'Draw Trendline
GRAPHIC LINE (xmin,ymin) - (xMax,yMax)
GRAPHIC WAITKEY$
GRAPHIC WINDOW END hGraph
END FUNCTION
FUNCTION TrendLine(a() AS EXT,s AS EXT, o AS EXT) AS LONG
LOCAL i,n,sX,sY,sXY,sX2,sY2 AS EXT
n = UBOUND(a())
FOR i = 0 TO n
sX += a(i,0)
sy += a(i,1)
sXY += a(i,0) * a(i,1)
sx2 += a(i,0)^2
sY2 += a(i,1)^2
NEXT
s = (n * sXY - sX*sY)/(n*sX2 - sX^2)
o = (sY - s *sX)/n
END FUNCTION
'
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