#title Angle

{{{
기준치 z = (값 - 평균) / 표준편차
편차치 t = 10z +50

-> 편차치로 Slope를 구한다음

각도 = ATan(Slope) * 180/Pie;
}}}

x의 길이가 36, y 길이가 3이라면
{{{
angle <- atan(3/36) * (180/pi)
}}}

--https://stackoverflow.com/questions/1897704/angle-between-two-vectors-in-r
두 백터
{{{
angle <- function(x,y){
  dot.prod <- x%*%y 
  norm.x <- norm(x,type="2")
  norm.y <- norm(y,type="2")
  theta <- acos(dot.prod / (norm.x * norm.y))
  as.numeric(theta)
}

x <- as.matrix(c(2,1))
y <- as.matrix(c(1,2))
angle(t(x),y)          # Use of transpose to make vectors (matrices) conformable.
[1] 0.6435011
}}}

==== slope to angle ====
regression 결과가 이렇다면..
{{{
    x <- (1:length(y)) * (max(y) - min(y)) / length(y)
    m <- lm(y~x)
    pred <- predict(m, newdata=data.frame(x,y), interval = "predict", level=.9)
    agl <- atan(coef(m)[2]) * (180/pi)
}}}


{{{
A <- c(1,2,3,4,5)
B <- c(6,7,8,9,10)
acos(sum(A*B) / (sqrt(sum(A^2)) * sqrt(sum(B^2)))) * (180/pi)
}}}