What are subroutines?
The term “subroutine” is found in the realm of computing, but is just as apt in describing what we do in dance:

subroutine
n : a set sequence of steps, part of larger computer program

(our dance definition)
n : a set sequence of combinations, part of larger choreography occurring over the course of a song

Subroutines are combination sequences that have no fixed length, and function as stock phrases in dance. A collection of subroutines, often categorised by function, is called a subroutine library. The initiation of subroutines lies within the domain of the leading partner. Since each Lead possesses a library that is unique, it can be an advantage for a Follower to dance more than just one partner. Over time, a follower would accumulate experience with a wide variety of subroutines, thereby increasing her/his prospects of coping with new partners and subroutines on the dance floor.
 

Why do subroutines exist?
When a person first assumes the role of Lead, the learning curve is very steep because a great many things must be co-ordinated: dance timing, move selection, lead timing, positioning…

As you've experienced previously (see Simple Combinations), a single combination does not last a long time. If you had to assemble a sequence, combination by combination, a lot of mental effort would be expended just on move selection, with very little being left over for other aspects of dance. Ironically this mode of dancing is the ultimate in flexibility, as you'd be able to tailor your dancing precisely to suit the music and conditions as they occurred (if you had the mental headroom to do so).

On the other hand a full-blown routine lasting one track, once naturalised, requires hardly any processing power on the Lead's part. However its inflexibility would render it unresponsive to changes in music and space on the dance floor.

It is the equivalent of spelling “h-e-l-l-o- -w-o-r-l-d”as compared with saying “hello world”.

Subroutines offer a compromise between the two extremes of spontaneous and predetermined choreography (the single words “world” and “hello”). Their modularity reduces the amount of mental effort expended on move selection while still allowing the flexibility to cope with arising situations.
 

Classification and Properties of Subroutines
Subroutines generally fall under three categories:

1. those requiring no prior dance knowledge;
2. those requiring general dance knowledge;
3. those requiring knowledge specific to that particular subroutine.

Other categories of the library could refer to the regional style (Dominican, Puerto Rican), timing (regular, syncopated) or look and feel (hot, cool, smooth). Irrespective of category, they all have three properties in common.

Duration
Short subroutines place a greater emphasis on move selection and allow you to be more adaptable. Longer subroutines allow you to focus on the execution of the patterns, at the expense of flexibility. Most Latin music genres are played in musical phrases comprising an even number of bars or music. Subroutines can be in-phrase (even number of bars) or cross-phrase (odd number of bars).

Shape and Space
A subroutine has a particular shape and takes up a certain amount of space at a given point in time.

Points of flexibility
(The single-most overlooked property of a subroutine)
Temporal: these are places where a subroutine may be extended, truncated or altered. Elements can be performed at half speed, double speed, or have their timing structure changed.
Spatial: these are places where a subroutine can be reoriented, bent or flexed to create a different look, or to take advantage of unanticipated openings on the floor.
 

Let's look at Sequence 1 (Octopus, Simple Combinations: Core) as an example. We know that the basic version takes two bars of music (one per partner) and is therefore in-phrase. It is almost circular (slightly oval) in shape when viewed from above.

Flexing it temporally
One of the component combinations could be performed at double speed and the other 50% slower, resulting in a ½ bar: 1½ bar ratio. This would keep you in phrase with the music. Alternatively, a component combination could be performed at half normal speed resulting in a 2 bar: 1 bar ratio. This would be used to cross the music phrase.

Flexing it spatially:
You could change your direction of travel from a clockwise orbit to a linear path to your right (be sure to keep your partner with you), flattening the sequence shape on one side. You might, in the interest of preserving your partner's safety, use it to deny other people's access to a particular space by positioning your body as a passive barrier.
 

How are subroutines used?
The use of subroutines is a realm without right or wrong. All I can offer are some thoughts and suggestions for you to consider.

The simplest way is to use them one after another until you've run through your whole library, and then start all over again. Concatenation is easy, but it isn't exactly elegant.

I recommend that subroutines be used against a backdrop of basic steps and simple figures. The basic steps do more to distinguish one dance genre from another than complex patterns. They act as periods of calm, allowing you to:

Acquaint yourself with your partner
It is a social dance we're talking about. You should take the time to accustom yourself with your partner's movement and timing style, understand her/his level of proficiency and habits.

Listen to the passage of music
Dance is movement to music, so it makes sense to listen to what's being played and then interpret it. It's a chance for both of you to inject your personality into the song. Don't pass it up.

Increase the dynamism in your dancing by providing contrast
Doing just basics or complex subroutines all the time gives your dancing only one activity level, sedate or frenetic respectively. It's like eating baby food; okay when you start, but the lack of texture makes it a little tiresome towards the end. Changing activity levels changes the texture of dance, keeping it interesting.

Assess the current environment
Taking stock of what's happening around you, the proximity of other dancers, the shapes of spaces on the dance floor, helps you decide which subroutine to use and when.

These are the factors you might consider when deciding which subroutine to apply:

• amount of space available;
• the shape of that space;
• your own ability;
• your partner's ability;
• the music;
• the feel you'd like to create.

Yep. Up until now we have not considered your own ability to perform the necessary tasks for the completion of a subroutine. Are you proficient enough and are the conditions right for you to be able to perform the pattern safely and successfully?

If it's a definite “yes” then great. If it's a “maybe”, then think whether it's still safe enough to risk your partner (and yourself). If it's a “no”, then pick a more suitable one.