if(!require(aaltobda)){
  install.packages("remotes")
  remotes::install_github("avehtari/BDA_course_Aalto", subdir = "rpackage", upgrade="never")
  library(aaltobda)
}

mean_vector = c(0, 10)
covariance_matrix = matrix(c(4, 12, 12, 100), nrow=2, ncol=2)
to_calculate = matrix(c(1, 2, 3, 4), nrow=2, ncol=2)

print(class(to_calculate)) # prints: [1] "matrix" "array"

# We can force to_calculate to have only one class by uncommenting the line below.
#attr(to_calculate, "class") = 'matrix'

# If we don't force the to_calculate matrix to have only one class,
# we get this error when calling dmvnorm:
# Error in if (class(x) == "matrix") { : the condition has length > 1
marginals = dmvnorm(to_calculate, mean_vector, covariance_matrix, log = TRUE)

print(marginals)

# This code demonstrates the problem:
if (class(to_calculate) == 'matrix'){
  print(1)
} else {
  print(2)
}

# The code can be fixed like this:
if ('matrix' %in% class(to_calculate)){
  print(1)
} else {
  print(2)
}