3a_Writing_your_own_start_script.Rmd

---
title: "Writing your own start script"
subtitle: MAgPIE model development team (magpie@pik-potsdam.de)
date: "`r format(Sys.time(), '%d %B, %Y')`"
author: Abhijeet Mishra (mishra@pik-potsdam.de)
output:
  rmarkdown::github_document:
    toc: yes
---

# 1 Introduction

## 1.1 Why use your own starting script

MAgPIE reads its specified configuration file just before starting a model run. Editing these config files by hand maybe practical in cases where a user is making one run at a time but more often than not, users may have to work with a combination of different settings for the model. 

For example, a user may want to run two different trade scenarios in MAgPIE (self sufficiency based & free-trade) and along with this, a user may also want to run  two different policy scenarios (with and without CO2 prices). In this case, the total number of runs needd is 2\*2=4. In such cases, editing config files by hand is not advisable. Here, a good programming practice would be to rather change these config files using an R script which changes the config settings in automatised manner. 

## 1.2 Relevence to MAgPIE 

With MAgPIE having a lot of modules and settings which can be changed and used in various combinations, it becomes imperative that a user be able to change a lot of settings concurrently. This can be achieved by changing the config file (from tutorial series 3) for turning on or off module realizations and other settings.

## 1.3 Learning objectives

The goal of this exercise is to write your own starting script. After completion of this exercise, you'll be able to:

\

1. Understand how standard MAgPIE starting scripts work.

\

2. Write your own starting script.
\

\newpage
# 2. Getting started

Before we write our own starting script, it is important to know what a start script really does. Let's have a look at tutorial 3 again and see the last part of the exercise where we started a model run. For this, we first opened a command line prompt in the cloned MAgPIE folder and ran the following command: \

```{r, eval=FALSE}
Rscript start.R
```

This operation calls the **start.R** script from the folder where MAgPIE is cloned. 

Then we selected option 1 (**default**) before making the model run. 

The **start.R** script looks for the **start** folder located in the **scripts** folder and displays all the R scripts contained inside. 

Looking into the contents of **scripts/start** you'll notice an R script by the name of **default.R** which was used to carry out the operation we selected earlier. 

Let us have a look at the inner workings of this **default.R** script before we write our own starting script.

# 3 Structure of default start script

If you navigate to **scripts/start/default.R**, you'll see that the **default.R** script has the following structure:
(you can open this script in R or even in a plain-text editor). \

```{r, eval=FALSE}
######################################
#### Script to start a MAgPIE run ####
######################################

# Load start_run(cfg) function which is needed to start MAgPIE runs
source("scripts/start_functions.R")

#start MAgPIE run
start_run(cfg="default.cfg")

```

This is a basic script with no complex structure but let's go through this step-by-step. The first line is:\

```{r, eval=FALSE}
source("scripts/start_functions.R")
```

This tells the R environment to source **start_functions.R** from the **scripts** folder. Due to time constraints, we won't look into what start_functions.R does but we just have to remember that this script loads the config file and then loads start_run function with this config which is needed to start MAgPIE runs.

Moving forward, the second line is: \

```{r, eval=FALSE}
start_run(cfg="default.cfg")
```

The **start_run()** function sourced from above is the used to start the run.

\newpage
# 4 Writing our own start script

Before we start writing our own start script, let's first discuss which settings we'd like to change using this start script. For the sake of simplicity, let's just try to change two settings. We'll make a total of 2*2=4 MAgPIE runs with following changes:

1.  Making runs with two different **trade** module realizations.

\
\

2.  Making runs with two different **forestry** module realizations.

\
\


## 4.1 Creating a start script from scratch

There are many ways in which you can initialize an R script that can be used as a starting script. The easiest way however is to just make a copy of one of the existing start scripts inside the **scripts/start** folder.

For this, just copy the **default.R** script in **scripts/start** folder and paste it within the same folder. Now rename this copied file to a name of your liking. For this workshop's purpose, let's call is **magpie_workshop.R**.

As **magpie_workshop.R** is just a renamed version of **default.R**, the contents are the same and we'll now start making changes to this **magpie_workshop.R** script. Users are now requested to open this **magpie_workshop.R** script in R or in a text editor of their choice. 

The contents should look like this: \

```{r, eval=FALSE}
######################################
#### Script to start a MAgPIE run ####
######################################

# Load start_run(cfg) function which is needed to start MAgPIE runs
source("scripts/start_functions.R")

#start MAgPIE run
start_run(cfg="default.cfg")

```


## 4.2 Importance of documenting your code/script

At this point, we'd like to emphasize upon the importance of code documentation and comments within the code.

The comments in your code would help you communicate to another user what your script is trying to do and what a certain fragment of code does. Not to mention that your future self will thank you for a well documented/commented code. Always remember to add appropriate comments to your code. 

Imagine if the **default.R** script mentioned above looked like this: \

```{r, eval=FALSE}
source("scripts/start_functions.R")
start_run(cfg="default.cfg")

```

Without any background information and documentation/comments, it is difficult to figure out what this piece of code is trying to do. Hence, it is always a good practice to document your code appropriately. 

Also remember that *code never lies, comments sometimes do*, so keep your comments as accurate and precise as possible.

## 4.3 Editing your start script

Now that we have the importance of documenting your code out of the way, lets go back to writing our script.

As we still want to make changes to the **config** before starting a run, lets delete the following line which starts the MAgPIE run as we don't need it for now (we'll need it in the end): \

```{r, eval=FALSE}
#start MAgPIE run
start_run(cfg="default.cfg")

```

Your script should now look like this: \

```{r, eval=FALSE}
###########################################################
#### Some header which explains what this script does  ####
###########################################################

# Load start_run(cfg) function which is needed to start MAgPIE runs
source("scripts/start_functions.R")
```

Now, we'll source the **default config** which you had changed in tutorial 3. To do so, add the following line to your script: \

```{r, eval=FALSE}
# Source the default config at this stage and then over-write it before starting the run.
source("config/default.cfg")
```

Remember that the above line just loads the object called **cfg** in R environment. Contents of this **cfg** object can be found in Table 1 from tutorial 3.

Your script should now look like this: \

```{r, eval=FALSE}
###########################################################
#### Some header which explains what this script does  ####
###########################################################

# Load start_run(cfg) function which is needed to start MAgPIE runs
source("scripts/start_functions.R")

# Source the default config at this stage and then over-write it before starting the run.
source("config/default.cfg")  
```

At this stage, when the script is called, it loads **start_run()** function and also loads the object **cfg** in R environment. Before submitting the run with **start_run()**, we'll make changes to the **default config** loaded in R environment. 

### 4.3.1 Adding basic settings

Lets add some basic settings before moving to the main changes. These changes would be made to the **cfg** object and we'll use the notation **cfg$\<some_setting\>** for this purpose (Ref. Table 1 from tutorial 3 for details). 

Go ahead and add the following lines in your **magpie_workshop.R** script: \

```{r, eval=FALSE}
# Change results folder name
cfg$results_folder <- "output/:title:"

# Change time step settings
cfg$gms$c_timesteps <- 5

# Updating the desired output generation automatically after run
cfg$output <- c("rds_report","interpolation")
```

You'll see that we had already changed these settings by hand in tutorial 3. Here, these settings will be changed in **default config** using the **magpie_workshop.R** starting script which should look like this now: 
\

```{r, eval=FALSE}
###########################################################
#### Some header which explains what this script does  ####
###########################################################

# Load start_run(cfg) function which is needed to start MAgPIE runs
source("scripts/start_functions.R")

# Source the default config at this stage and then over-write it before starting the run.
source("config/default.cfg")  

# Change results folder name
cfg$results_folder <- "output/:title:"

# Change time step settings
cfg$gms$c_timesteps <- 5

# Updating the desired output generation automatically after run
cfg$output <- c("rds_report","interpolation")
```

### 4.3.2 Adding loop(s)

We'll now write a loop to go over the different combinations of module realiazations. As stated earlier, we'll make 4 runs with changes to trade module and forestry module. Figure 1 describes and explains the available module realizations for these two modules.

![Module setting combinations](figures/module-settings.png)

\newpage

The loop we write should change the config based on which module realization we choose. Here, lets try making runs with the following combinations:

1. Trade default + Forestry default
2. Trade default + Forestry alt
3. Trade alt + Forestry default
4. Trade alt + Forestry alt

To do so, the loop should go two times over trade module realizations and then for each of theses instances, two times over the forestry module realizations. In principle, this loop's general structure should look like this:  \

```{r, eval=FALSE}

for(trade_setting in c("default_trade","alt_trade")){
  
  for(forestry_setting in c("default_forestry","alt_forestry")){
    
    change_trade_module_realization   ## Updates cfg
    
    change_forestry_module_realization  ## Updates cfg

    change_title_according_to_run_setting
    
    ## cfg has been changed further at his stage, start the run
    start_the_run  
  }
}
```

Hence our working loop should look like this (adding **start_run** in the loop which we deleted earlier): \

```{r, eval=FALSE}
# Starting trade loop
for(trade_setting  in c("selfsuff_reduced","free_apr16")){
  # Starting forestry loop
  for(forestry_setting  in c("dynamic_may20","static_sep16")){
    
    # Set trade realization
    cfg$gms$trade <- trade_setting 
    
    # Set forestry realization
    cfg$gms$forestry <- forestry_setting 
    
    # Changing title flags
    if(trade_setting  == "selfsuff_reduced") trade_flag="resTrade"
    if(trade_setting  == "free_apr16") trade_flag="freeTrade"
    if(forestry_setting  == "dynamic_may20") forestry_flag = "dynFor"
    if(forestry_setting  == "static_sep16") forestry_flag = "statFor"
    
    # Updating default tile
    cfg$title<- paste0("MAgPIE","_",trade_flag,"_",forestry_flag)
    
    ## cfg has been changed further at his stage, start the run
    start_run(cfg=cfg)  
  } # <- Closing forestry loop
} # <- Closing trade loop
```

\newpage

The final **magpie_workshop.R** script should look like this: \

```{r, eval=FALSE}
###########################################################
#### Some header which explains what this script does  ####
###########################################################

# Load start_run(cfg) function which is needed to start MAgPIE runs
source("scripts/start_functions.R")

# Source the default config at this stage and then over-write it before starting the run.
source("config/default.cfg")  

# Change results folder name
cfg$results_folder <- "output/:title:"

# Change time step settings
cfg$gms$c_timesteps <- 5

# Updating the desired output generation automatically after run
cfg$output <- c("rds_report","interpolation")

# Starting trade loop
for(trade_setting  in c("selfsuff_reduced","free_apr16")){
  # Starting forestry loop
  for(forestry_setting  in c("dynamic_may20","static_sep16")){
    
    # Set trade realization
    cfg$gms$trade <- trade_setting 
    
    # Set forestry realization
    cfg$gms$forestry <- forestry_setting 
    
    # Changing title flags
    if(trade_setting  == "selfsuff_reduced") trade_flag="resTrade"
    if(trade_setting  == "free_apr16") trade_flag="freeTrade"
    if(forestry_setting  == "dynamic_may20") forestry_flag = "dynFor"
    if(forestry_setting  == "static_sep16") forestry_flag = "statFor"
    
    # Updating default tile
    cfg$title<- paste0("MAgPIE","_",trade_flag,"_",forestry_flag)
    
    ## cfg has been changed further at his stage, start the run
    start_run(cfg=cfg)  
  } # <- Closing forestry loop
} # <- Closing trade loop
```

\newpage

# 5 Starting MAgPIE with custom R script

So far, we have learned:

\

1. How standard MAgPIE starting scripts work.

\

2. How to write our own starting script.

\


Now that we have created our own **magpie_workshop.R** starting script in the folder **scripts/start**, we are ready to test our script and make a MAgPIE run.

To do so, windows users can go to the folder where MAgPIE was cloned and open a command line prompt there. For windows users, this can be done by typing **cmd** or **powershell** at the address bar of the folder where MAgPIE was cloned and then pressing return/enter. 

For mac users (if right click -> open terminal setting is not enabled), Head into System Preferences and select Keyboard > Shortcuts > Services. Find "New Terminal at Folder" in the settings and click the box. Now, when you're in Finder, just right-click a folder and you're shown the open to open Terminal. 

In the command prompt (or powershell or terminal) you just opened, use the following command: \
```{r, eval = FALSE}
Rscript start.R
``` 

You'll now see a bunch of R scripts on your command prompt, based on which the model can be run. 

We will used recently created **magpie_workshop.R** script which uses **default.cfg** as starting settings and then changes these settings automatically.

In order to start the run, Select option number corresponding to **magpie_workshop** to tell the model that we want to make runs according to our custom start script and then option 1 again (***Direct execution***). 

This will start^[To stop a run you can use the key combination **ctrl** + **c** on windows machines.] the model run on your local machine.