Can't combine tune and hardcoded values in tune grid

[cimentadaj]

Running this:

library(tidymodels)
devtools::load_all()
library(mlbench)
data(Ionosphere)
Ionosphere <- Ionosphere %>% select(-V2) %>% mutate(cont = 1:nrow(.)) %>% as_tibble()

svm_mod <-
  svm_rbf(cost = tune(), rbf_sigma = -0.25) %>%
  set_mode("classification") %>%
  set_engine("kernlab")

iono_rec <-
  ~ recipe(Class ~ ., data = .)  %>%
    step_zv(all_predictors()) %>%
    step_mutate(V1 = factor(V1), Class = factor(Class)) %>% 
    step_dummy(V1) %>% 
    step_range(matches("V1_")) %>% 
    step_ns(cont, deg_free = tune())

tflow <-
  Ionosphere %>%
  tidyflow(seed = 4943) %>%
  plug_split(initial_split) %>% 
  plug_recipe(iono_rec) %>%
  plug_resample(bootstraps, times = 30) %>%
  plug_model(svm_mod) %>% 
  plug_grid(grid_latin_hypercube,
            cost = cost(c(-10, 10)),
            size = 1)

t1 <- tflow %>% fit()

Doesn't run. The error comes from tune_grid, as discussed at tidymodels/tune#150

[cimentadaj]

This is fixed by specifying the fixed value in svm_mod as positive. You can't have negative values in the kernel.