Merge pull request #295 from mrc-ide/mrc-4318

Support for differentiation of parameters in DSL

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: odin
 Title: ODE Generation and Integration
-Version: 1.5.3
+Version: 1.5.4
 Authors@R: c(person("Rich", "FitzJohn", role = c("aut", "cre"),
                     email = "rich.fitzjohn@gmail.com"),
              person("Thibaut", "Jombart", role = "ctb"),

R/ir_parse.R

@@ -479,38 +479,67 @@ ir_parse_packing_internal <- function(names, rank, len, variables,
 ## few different places.  It might be worth trying to shift more of
 ## this classification into the initial equation parsing.
 ir_parse_features <- function(eqs, debug, config, source) {
-  is_update <- vlapply(eqs, function(x) identical(x$lhs$special, "update"))
-  is_deriv <- vlapply(eqs, function(x) identical(x$lhs$special, "deriv"))
-  is_output <- vlapply(eqs, function(x) identical(x$lhs$special, "output"))
-  is_dim <- vlapply(eqs, function(x) identical(x$lhs$special, "dim"))
+  is_lhs_update <- vlapply(eqs, function(x) identical(x$lhs$special, "update"))
+  is_lhs_deriv <- vlapply(eqs, function(x) identical(x$lhs$special, "deriv"))
+  is_lhs_output <- vlapply(eqs, function(x) identical(x$lhs$special, "output"))
+  is_lhs_dim <- vlapply(eqs, function(x) identical(x$lhs$special, "dim"))
   is_user <- vlapply(eqs, function(x) !is.null(x$user))
   is_delay <- vlapply(eqs, function(x) !is.null(x$delay))
   is_interpolate <- vlapply(eqs, function(x) !is.null(x$interpolate))
   is_stochastic <- vlapply(eqs, function(x) isTRUE(x$stochastic))
   is_data <- vlapply(eqs, function(x) !is.null(x$data))
-  is_compare <- vlapply(eqs, function(x) identical(x$lhs$special, "compare"))
+  is_lhs_compare <- vlapply(eqs,
+                            function(x) identical(x$lhs$special, "compare"))
+  is_user_differentiate <- vlapply(eqs,
+                                   function(x) isTRUE(x$user$differentiate))
 
   ## We'll support other debugging bits later, I imagine.
   is_debug_print <- vlapply(debug, function(x) x$type == "print")
 
-  if (!any(is_update | is_deriv)) {
+  if (!any(is_lhs_update | is_lhs_deriv)) {
     ir_parse_error("Did not find a deriv() or an update() call",
                    NULL, NULL)
   }
 
-  list(continuous = any(is_deriv),
-       discrete = any(is_update),
-       mixed = any(is_update) && any(is_deriv),
-       has_array = any(is_dim),
-       has_output = any(is_output),
+  continuous <- any(is_lhs_deriv)
+  has_compare <- any(is_lhs_compare)
+  has_array <- any(is_lhs_dim)
+  has_derivative <- any(is_user_differentiate)
+
+  ## Most of these constraints go away later, might as well throw them
+  ## early though; we could put it into a preliminary check for
+  ## differentiability but in some ways thast just complicates things.
+  if (has_derivative) {
+    if (!has_compare) {
+      ## (this one is fundamental; this just can't be done!
+      ir_parse_error("You need a compare expression to differentiate!",
+                     ir_parse_error_lines(eqs[is_user_differentiate]), source)
+    }
+    if (continuous) {
+      ir_parse_error("Can't use differentiate with continuous time models",
+                     ir_parse_error_lines(eqs[is_user_differentiate]), source)
+    }
+    if (has_array) {
+      ir_parse_error(
+        "Can't use differentiate with models that use arrays",
+        ir_parse_error_lines(eqs[is_user_differentiate | is_lhs_dim]), source)
+    }
+  }
+
+  list(continuous = continuous,
+       discrete = any(is_lhs_update),
+       mixed = any(is_lhs_update) && continuous,
+       has_array = has_array,
+       has_output = any(is_lhs_output),
        has_user = any(is_user),
        has_delay = any(is_delay),
        has_interpolate = any(is_interpolate),
        has_stochastic = any(is_stochastic),
        has_data = any(is_data),
-       has_compare = any(is_compare),
+       has_compare = has_compare,
        has_include = !is.null(config$include),
        has_debug = any(is_debug_print),
+       has_derivative = has_derivative,
        initial_time_dependent = NULL)
 }
 
@@ -1040,7 +1069,9 @@ ir_parse_expr_rhs_user <- function(rhs, line, source) {
     ir_parse_error("Only first argument to user() may be unnamed", line, source)
   }
 
-  m <- match.call(function(default, integer, min, max, ...) NULL, rhs, FALSE)
+  m <- match.call(
+    function(default, integer, min, max, differentiate, ...) NULL,
+    rhs, FALSE)
   extra <- m[["..."]]
   if (!is.null(extra)) {
     ir_parse_error(sprintf("Unknown %s to user(): %s",
@@ -1063,12 +1094,23 @@ ir_parse_expr_rhs_user <- function(rhs, line, source) {
   if (length(deps$variables) > 0L) {
     ir_parse_error("user() call must not reference variables", line, source)
   }
-  ## TODO: the 'dim' part here is not actually known yet!
+
+  integer <- m$integer %||% FALSE
+  differentiate <- m$differentiate %||% FALSE
+
+  if (differentiate && integer) {
+    ir_parse_error("Can't differentiate integer parameters",
+                   line, source)
+  }
+
+  ## NOTE: the 'dim' part here is not actually known yet!
   user <- list(default = m$default,
                dim = FALSE,
-               integer = m$integer %||% FALSE,
+               integer = integer,
                min = m$min,
-               max = m$max)
+               max = m$max,
+               differentiate = differentiate)
+
   list(user = user)
 }
 

inst/schema.json

@@ -204,6 +204,7 @@
                 "has_stochastic": { "type": "boolean" },
                 "has_include": { "type": "boolean" },
                 "has_debug": { "type": "boolean" },
+                "has_derivative": { "type": "boolean" },
                 "initial_time_dependent": { "type": "boolean" }
             },
             "required": ["discrete", "has_array", "has_output", "has_user",

tests/testthat/test-parse2-differentiate.R

@@ -0,0 +1,64 @@
+test_that("Can parse with differentiable parameters", {
+  ir <- odin_parse({
+    initial(x) <- 1
+    update(x) <- rnorm(0, 0.1)
+    d <- data()
+    compare(d) ~ normal(0, scale)
+    scale <- user(differentiate = TRUE)
+  })
+
+  d <- ir_deserialise(ir)
+  expect_true(d$features$has_derivative)
+})
+
+
+test_that("can't differentiate integer parameters", {
+  expect_error(odin_parse({
+    initial(x) <- 1
+    update(x) <- rnorm(0, 0.1)
+    d <- data()
+    compare(d) ~ normal(x, scale)
+    scale <- user(differentiate = TRUE, integer = TRUE)
+  }),
+  "Can't differentiate integer parameters\\s+scale <-")
+})
+
+
+test_that("can't differentiate without compare", {
+  expect_error(
+    odin_parse({
+      initial(x) <- 1
+      update(x) <- rnorm(x, scale)
+      scale <- user(differentiate = TRUE)
+    }),
+    "You need a compare expression to differentiate!\\s+scale <-")
+})
+
+
+test_that("can't differentiate continuous time models", {
+  expect_error(
+    odin_parse({
+      initial(x) <- 1
+      deriv(x) <- 1
+      d <- data()
+      compare(d) ~ normal(x, scale)
+      scale <- user(differentiate = TRUE)
+    }),
+    "Can't use differentiate with continuous time models\\s+scale <-")
+})
+
+
+test_that("can't differentiate models with arrays", {
+  err <- expect_error(
+    odin_parse({
+      initial(x[]) <- 1
+      update(x[]) <- rnorm(x, 1)
+      dim(x) <- 5
+      d <- data()
+      compare(d) ~ normal(sum(x), scale)
+      scale <- user(differentiate = TRUE)
+    }),
+    "Can't use differentiate with models that use arrays")
+  expect_match(err$message, "dim(x) <-", fixed = TRUE)
+  expect_match(err$message, "scale <-", fixed = TRUE)
+})