सवर्णदीर्घ-सन्धि

It is the lengthening of homogeneous vowels occurring one after another.

• अ/आ + अ/आ = आ 
• इ/ई + इ/ई = ई
• उ/ऊ + उ/ऊ = ऊ
• ऋ/ॠ + ऋ/ॠ = ॠ ( or ऋ ) 
• ऋ/लृ + लृ = ॠ ( or लृ ) - This is because there is no लॄ vowel used in संस्कृत .   

Note: For explaining the occurrence of सन्धि -  '+' sign ;for the सन्धि formed - '=' sign will be used hereafter for all सन्धिs.