calcular.optimo.derivada: no visible global function definition for
  'loess'
calcular.optimo.pendiente: no visible global function definition for
  'loess'
iconfianza.aritmetica: no visible global function definition for
  'qnorm'
iconfianza.aritmetica: no visible global function definition for 'var'
iconfianza.completo: no visible global function definition for 'var'
iconfianza.completo: no visible global function definition for 'qnorm'
iconfianza.percentil.boot : quantile.fun: no visible global function
  definition for 'quantile'
iconfianza.percentil.boot : quantile.fun: no visible global function
  definition for 'var'
iconfianza.percentil.boot: no visible global function definition for
  'quantile'
iconfianza.percentil.kc: no visible global function definition for
  'qnorm'
iconfianza.x: no visible global function definition for 'qnorm'
iconfianza.x: no visible global function definition for 'var'
plot.epidemic: no visible global function definition for 'par'
plot.epidemic: no visible global function definition for 'matplot'
plot.epidemic: no visible global function definition for 'axis'
plot.epidemic: no visible global function definition for 'points'
plot.epidemic: no visible global function definition for 'legend'
plot.flu: no visible global function definition for 'par'
plot.flu: no visible global function definition for 'rgb'
plot.flu: no visible global function definition for 'runif'
plot.flu: no visible global function definition for 'matplot'
plot.flu: no visible global function definition for 'axis'
plot.flu: no visible global function definition for 'abline'
plot.flu: no visible global function definition for 'legend'
plot.flu: no visible global function definition for 'text'
Undefined global functions or variables:
  abline axis legend loess matplot par points qnorm quantile rgb runif
  text var
Consider adding
  importFrom("grDevices", "rgb")
  importFrom("graphics", "abline", "axis", "legend", "matplot", "par",
             "points", "text")
  importFrom("stats", "loess", "qnorm", "quantile", "runif", "var")
to your NAMESPACE file.