Improve predict_mixture

description

Multiple changes to predict_mixture.

• The concentration vectors are checked for NAs, which raise an error when found.
• The use of drc::ED() was replaced with a custom inverse weibull function, which does the same but better.
• predict_mixture() accepts multiple values for the concentration of the second toxicant. Both concentration vectors must be the same length.
• predict_mixture() returns a data frame with the concentrations and effects. Previously it was only a vector of effects.
• predict_mixture() received a new argument "effect_max" which scales the returned effect values.
• Renamed the arguments of predict_mixture() to use underscore letters a and b instad of 1 and 2. For example model_1 is now model_a.

system details

• RStudio Version: Version 1.2.5033
• R Version: 3.6.3
• OS Version: Windows 10 x64 (build 18363)

checklist

• This merge introduces new features.
  • new features are documented
  • new features have tests
• update documentation including examples (if necessary)
• update and polish NEWS.md
• update version in DESCRIPTION
• update date in DESCRIPTION
• no remaining TODO, FIXME, or debug prints anywhere in the source files
• devtools::document()
• devtools::check() without errors or warnings

tests/testthat/test-predict_mixture.R

@@ -55,6 +55,17 @@ test_that("results have not changed", {
     reference <- c(88.2698383, 79.9617127, 78.1574808, 65.7999834, 0.3861678, 0)
     expect_equal(new, reference, tolerance = 1e-5)
 
+    # diverse concentration_2 and custom effect_max
+    new <- predict_mixture(
+        model_1,
+        model_2,
+        c(0, 0.01, 0.1, 1, 7, 15),
+        c(0, 0.02, 0.2, 2, 14, 30),
+        0.3,
+        42
+    )$mixture_effect
+    reference <- c(88.2698383, 79.9617127, 78.1574808, 65.7999834, 0.3861678, 0) * 0.42
+    expect_equal(new, reference, tolerance = 1e-5)
 })