A Shiny app made with Grind

The Shiny environment in R allows one to make interactive apps of for particular models. For instance check the Shiny Lotka Volterra model that was made with this app.R script. You can also run this script in RStudio by sourcing it or clicking Run App. The script app.R can also be downloaded from the Grind directory. You have to install the shiny R-package beforehand.

source("grind.R")

## grind.R (21-01-2024) was sourced

library(shiny)

model <- function(t, state, parms) {
  with(as.list(c(state,parms)), {
    dR <- r*R*(1 - R/K) - a*R*N
    dN <- c*a*R*N - delta*N
    return(list(c(dR, dN)))  
  }) 
}  
p <- c(r=1,K=1,a=1,c=1,delta=0.5) 
s <- c(R=1,N=0.1)

ui <- fluidPage(
  titlePanel("Lotka Volterra model"),
  sidebarLayout(
    sidebarPanel(
      sliderInput(inputId=names(s[1]),label=names(s[1]),min=0,max=10,step=0.01,value=as.numeric(s[1])),
      sliderInput(inputId=names(s[2]),label=names(s[2]),min=0,max=10,step=0.01,value=as.numeric(s[2])),
      sliderInput(inputId=names(p[1]),label=names(p[1]),min=0,max=p[1]*10,step=p[1]*0.01,value=p[1]),
      sliderInput(inputId=names(p[2]),label=names(p[2]),min=0,max=p[2]*10,step=p[2]*0.01,value=p[2]),
      sliderInput(inputId=names(p[3]),label=names(p[3]),min=0,max=p[3]*10,step=p[3]*0.01,value=p[3]),
      sliderInput(inputId=names(p[4]),label=names(p[4]),min=0,max=p[4]*10,step=p[4]*0.01,value=p[4]),
      sliderInput(inputId=names(p[5]),label=names(p[5]),min=0,max=p[5]*10,step=p[5]*0.01,value=p[5])
    ),

    mainPanel(
      h4("R '= r*R*(1 - R/K) - a*R*N"),
      h4("N '= c*a*R*N - delta*N"),
      plotOutput(outputId="grind"),
      radioButtons("radio", "Grind output:",c("Time plot"=0,"Nullclines"=1,"Trajectory"=2,"Portrait"=3,"Steady state"=4),selected=1,inline=TRUE),
      fluidRow(
      column(3,numericInput(inputId="tmax",label="Tmax",value=100)),
      column(3,numericInput(inputId="tstep",label="Tstep",value=0.1,step=0.1))),
      textOutput("log")
    )
  )
)

server <- function(input, output) {
  output$grind <- renderPlot({
    radiob <- input$radio
    for (i in names(s)) s[i] <- input[[i]]
    for (i in names(p)) p[i] <- input[[i]]
    tmax <- input$tmax
    tstep <- input$tstep
    xmax <- 1.1*max(p["K"],p["delta"]/(p["c"]*p["a"]),s["R"])
    ymax <- 1.1*max(p["r"]/p["a"],s["N"])
    output$log <- renderText("")
    if (radiob == 0) {
      f <- run(tmax=tmax,tstep=0.1,odes=model,state=s,parms=p)
      output$log <- renderText({paste("Ended in R =",round(f[1],5),"N =",round(f[2],5),sep=" ")})
    }
    else if (radiob <= 2) {
      plane(xmax=xmax,ymax=ymax,odes=model,state=s,parms=p,eps=-.001)
      if (radiob == 2) {
        f <- run(tmax=tmax,tstep=tstep,odes=model,state=s,parms=p,traject=TRUE)
        output$log <- renderText({paste("Ended in R =",round(f[1],5),"N =",round(f[2],5),sep=" ")})
      }
    }
    else if (radiob == 3) plane(xmax=xmax,ymax=ymax,tmax=tmax,tstep=tstep,odes=model,state=s,parms=p,eps=-.001,portrait=TRUE)
    else {
      plane(xmax=xmax,ymax=ymax,odes=model,state=s,parms=p,eps=-.001)
      f <- newton(state=s,parms=p,odes=model,plot=TRUE,positive=TRUE)
      if (is.null(f)) output$log <- renderText({"No convergence: start closer to a steady state"})
      else output$log <- renderText({paste("Converged into R =",round(f[1],5),"N =",round(f[2],5),sep=" ")})
    }
  })
}

shinyApp(ui = ui, server = server)