Adapted from Chapter 5 of 'Saṅgītaratnākara - A Study' by R.Rangaramanuja Ayyangar, 2nd Ed.
Janya rāga-s are derived from janaka rāga-s. It was the grāma-mūrcchanā concept that later developed into the
mēḷakarta - janya rāga system. In like manner, prastāra gleaned shreds of mārga tāla-s and chiselled them into
dēśī tāla-s and phrases of rhythm.
Druta (d), laghu (l), guru (g) and pluta (p), with mātrā values of 0.5, 1, 2 and 3 respectively, were elements of mārga tāla.
The prastāra listed all the permutation steps - each totalling to the mātrā value of the tāla - as the principal form of the tāla
was progressively reduced to a sarva-druta form.
The process of forming the prastāra table is now illustrated by considering an example of the pluta prastāra.
The principal form of this tāla has a single element, the pluta. This is equivalent of 6 druta-s with mātrā value of 3. Start by forming
a grid with the number of columns equal to the number of druta-s. In the first row, write the principal form of the tāla, aligning the elements to
the right. Then form each subsequent row as follows:
1. Scan the elements in the first row from the left to the right and select the first element that is not a druta.
2. Reduce this element by one level and take it down to the next row, while maintaining the column position. A pluta will reduce to a guru; a guru to a
laghu and laghu to a druta.
3. Now duplicate from the first row to the next, all elements that are to the right of the selected element.
4. Gather all the elements written on the second row and determine the mātrā value of the rūpam formed so far. All steps in the tāla
prastāra need to have the same mātrā count. With this objective in mind, to the left of the present rūpam, first add the highest
tāla element possible and then further druta-s, if required.
5. Repeat the above steps till a sarva-druta stage has been achieved.
The first six steps of the nineteen-step pluta prastāra are derived as shown below: