Data update

Task/Numeric-error-propagation/R/numeric-error-propagation.r

@@ -0,0 +1,61 @@
+#Plus-minus operator to generate uncertain numbers
+`%+-%` <- function(x, sigma){
+  if(!(is.numeric(x) & is.numeric(sigma))) stop("both arguments must be numeric")
+  structure(list("num"=x, "err"=sigma), class="uncertain")
+}
+
+#Coercing floats (or integers) to uncertain numbers (not used here)
+as.uncertain <- function(x) x%+-%0
+
+#Operators for uncertain numbers
+`+.uncertain` <- function(a, b){
+  if(isa(a, "uncertain") & isa(b, "uncertain")){
+    (a$num+b$num)%+-%sqrt(a$err^2+b$err^2)
+  }
+  else if(is.numeric(a)) b+a%+-%0
+  else if(is.numeric(b)) a+b%+-%0
+  else stop("non-numeric argument")
+}
+
+`-.uncertain` <- function(a, b){
+  if(isa(a, "uncertain") & isa(b, "uncertain")){
+    (a$num-b$num)%+-%sqrt(a$err^2+b$err^2)
+  }
+  else if(is.numeric(a)) b-a%+-%0
+  else if(is.numeric(b)) a-b%+-%0
+  else stop("non-numeric argument")
+}
+
+`*.uncertain` <- function(a, b){
+  if(isa(a, "uncertain") & isa(b, "uncertain")){
+    (a$num*b$num)%+-%a$num*b$num*sqrt((a$err/a$num)^2+(b$err/b$num)^2)
+  }
+  else if(is.numeric(a)) (b$num*a)%+-%abs(a*b$err)
+  else if(is.numeric(b)) (a$num*b)%+-%abs(b*a$err)
+  else stop("non-numeric argument")
+}
+
+`/.uncertain` <- function(a, b){
+  if(isa(a, "uncertain") & isa(b, "uncertain")){
+    (a$num/b$num)%+-%a$num*b$num*sqrt((a$err/a$num)^2+(b$err/b$num)^2)
+  }
+  else if(is.numeric(a)) (b$num/a)%+-%abs(b$err/a)
+  else if(is.numeric(b)) (a$num/b)%+-%abs(a$err/b)
+  else stop("non-numeric argument")
+}
+
+`^.uncertain` <- function(a,b){
+  if(!is.numeric(b)) stop("exponent must be integer or double")
+  (a$num^b)%+-%abs(b*a$err*a$num^(b-1))
+}
+
+#We need a print method to actually display uncertain numbers
+print.uncertain <- function(x) cat(x$num, "+/-", x$err)
+
+#The calculation
+x1 <- 100%+-%1.1
+y1 <- 50%+-%1.2
+x2 <- 200%+-%2.2
+y2 <- 100%+-%2.3
+
+d <- print(((x1-x2)^2+(y1-y2)^2)^(1/2))