उद्विभ्यां तपः

After the word तप 'to shine', when used intransitively and preceded by उत् or वि the आत्मनेपद affix is used.
As उत्तपते or वितपते विद्याया विद्यार्थी 'The scholar shines with knowledge.' But in transitive verbs, it is Parasmaipadi. As उत्तपति सुवर्णंसुवर्णकारः 'the goldsmith heats the gold,' वितपति पृष्ठं सविता 'the sun heats the back.'

Vart:- It must be stated that the terminations are of the atmanepada, though the verb ut-tapa or vi-tapa be transitive, when the object is some limb of one's own body. As उत्तपते पाणिम् or वितपते पाणिम् or पृष्ठम् 'he heats his own hand or back.' The word स्वाङ्ग means one's own body and not the paribhashika or the technical स्वाङ्ग meaning "a thing which not being liquid or gaseous and being capable of being perceived by the senses, and not being one produced by a change from the natural state, exists in a living being and though found elsewhere actually or at any particular time, had previously been known as existing in only a living being, or is found to have actually (not figuratively) the same relation to the being it is in, as a similar thing has to a living being." (See (IV. 1.54. स्वाङ्गाच्चोपसर्जनादसंयोगोपधात्). Therefore not so in the following देवदत्तो यज्ञदत्तस्य पृष्टमुत्तपति 'Devadatta heats the back of Yajnadatta.' When the preposition is other than ut or vi, parasmaipada affix is employed; as, निष्टपति.