How do I focus from the distraction of people who look attractive?

You might get catch-all advice for dealing with distractions but different styles of meditation deserve different solutions to distractions. Usually we can find a solution which compliments the style of your meditation and helps in working towards the goal of that meditation.

If you were doing samatha meditation and focusing on the breath the aim of this is to calm the mind. When you get distracted you could observe the distraction without judgement and then bring your awareness back to the breathing. This helps to teach you to remain calm when an opportunity for sense-indulgence occurs.

If your meditation was a type where you observe the changing nature of things the goal of this is to understand impermanence. When you are distracted you can observe that the distraction arose and then allow it to pass. This isn't just getting rid of the distraction, the distraction is just another opportunity to learn about impermanence.

Likewise if your goal is to see mathematical beauty then the distraction can be an opportunity for progressing to your goal. For example:

• What mathematical beauty can you see in being distracted?
• Can you see a mathematical beauty in returning from the distraction back to being aware of your surroundings?
• When you are distracted by a person perhaps you could look past the human beauty to see the mathematical beauty in their appearance.

I just came up with three approaches but you understand your meditation better than I do. I think you can come up with what's best for yourself.

Try skeleton meditation, don't even see the their skin. Always have your X-ray eyes on, seeing the flesh, bones, and organs of everything and everyone around you and yourself at all times. Turn them off when you feel you have enough.

Like it or not, you have been born into a male human body here on planet earth. You are in prime breeding age for a human male. The way I understand it, Buddha tried severe aestheticism regarding the senses and ruled that out. He decided that the middle-way was better that trying to force the mind, because the mind was a continuous, natural thing and was not force-able.

I would enjoy this experience, knowing it was transitory, an act by a human male, and being aware, resume the meditation as the feeling passed. Remember all things are transitory and will fade to nothingness in the end. This way your meditation will not be disturbed by your wanting "water to run uphill," which it will not do. Also remember, that you are presently fully enlightened, and it is only your "thinking machine" that blocks the realization of it.

You thinking seems to be tainted by Vipallasa

what is impermanent is taken to be permanent;

what is painful is taken to be pleasurable;

what is not self is taken to be a (or the) self; and

what is impure is taken to be pure.

^{- abopted from Vipallasa Sutta}

You should try to keep your mind free from Vipallasa then the path factor develops automatically.

Dawn, bhikshus, is the forerunner, the harbinger of sun-rise. Even so, bhikshus, for a monk this is the forerunner, the harbinger of the arising of the noble eightfold path, that is, accomplishment in wise attention.

Bhikshus, when a monk is accomplished in this wise attention, it is to be expected that he will cultivate the noble eightfold path, develop the noble eightfold path.

And how, bhikshus, does a monk who is accomplished in this wise attention cultivate the noble eightfold path, develop the noble eightfold path?

^{- Yoniso Manasikāra Sampadā Sutta}

.

When I walk around campus, I am in a meditative state; enjoying the surrounding nature and the mathematical fruit it bears.

.

And what, bhikshus, is right mindfulness? Here, bhikshus, a monk dwells exertive, clearly knowing, mindful, 
   observing the body in the body, 
      removing covetousness and displeasure in the world;
a monk dwells exertive, clearly knowing, mindful, 
     observing feelings in the feelings, 
        removing covetousness and displeasure in the world;
a monk dwells exertive, clearly knowing, mindful, 
   observing the mind in the mind, 
      removing covetousness and displeasure in the world; 
a monk dwells exertive, clearly knowing, mindful, 
   observing dharmas in the dharmas, 
      removing covetousness and displeasure in the world.
This, bhikshus, is called right mindfulness.

^{- (Magga) Vibhaṅga Sutta}

The key here is: "removing covetousness and displeasure in the world." So do not get attached or averse to what you see, hear, touch, taste, smell.

After I collect myself I can regain the motivation to pursue my maths and physics meditation, but this back and forth process feels burdening.

You can motivate yourself to study without attachment. This is developing intention but not crave for it.

Taking pleasure also is based on craving and is not without it. Alagaddupama Sutta

When I look at nature I try to understand impermanence

At a mundane level if you understand this is good. But this should be understood at the experiential level. For this you should do Vipassanā Meditation to see things as they are and not as you think they are or as you might want them to be.

My meditation also consists of trying to understand the objects that exists whether I am here or not (maths) and the transducer (physics) between these symbols/ideas and the temporal physical world.

Trying to understand is an intellectual game. This creates move Vipallasa and clouds your view than come out of it. You should keep to the 4 frames of reference without craving or aversion to the feelings that may arise. You should be equanimous to all that is felt and knowing it is impermanent.

How do I focus from the distraction of beautiful people?

Seeing Beauty in something is a Vipallasa. Everything ultimately disintegrates and falls apart. Therefore, beauty is temporary. You have to realise your mind analyses something and gives it an judgement as beautiful or ugly and to this evaluation you feel good when you see someone beautiful and feel bad when you see someone who is ugly. You have to be equanimous and seeing impermanence of the feeling that arises. More on this see this answer.

FORM

The ideal girl

And what, bhikshus, is the gratification with regards to form? Now, bhikshus, suppose there were a kshatriya girl or a brahmin girl or a householder’s girl, fifteen or sixteen years old, not too tall, not too short, not too thin, not too fat, not too dark, not too pale. Is this the time, bhikshus, when her beauty and complexion would be at its height?”28 “Yes, venerable sir.” “Now, bhikshus, the joy and pleasure that arise on account of that beauty and complexion is the gratification with regards to form.

And what, bhikshus, is the disadvantage with regards to form? This same woman here, later on, at eighty, ninety, or a hundred years old, crooked as a rafter, doubled up, supported by a walking-stick, tottering, frail, youth long gone, teeth broken, grey-haired, having little hair, bald, wrinkled, limbs all blotchy.

What do you think, bhikshus? Have her previous beauty and complexion vanished, the disadvantage (now) evident?”

“Yes, venerable sir.”

“This, bhikshus, is the disadvantage with regards to form.

Again, bhikshus, you might see this very same woman, afflicted, suffering and gravely ill, lying fouled in her own excrement and urine, lifted up by some and set down by others. What do you think, bhikshus? Have her previous beauty and complexion vanished, the disadvantage (now) evident?”

“Yes, venerable sir.”

“This, bhikshus, is the disadvantage with regards to form.

Again, bhikshus, you might see this very same woman as a corpse, cast aside in a charnel ground, dead for a day, dead for two days, dead for three days, bloated up, livid, and oozing with impurities.

What do you think, bhikshus? Have her previous beauty and complexion vanished, the disadvantage (now) evident?”

“Yes, venerable sir.”

“This, bhikshus, is the disadvantage with regards to form.

Again, bhikshus, you might see this very same woman as a corpse, cast aside in a charnel ground, eaten by crows, or being eaten by hawks, or being eaten by vultures, or being eaten by dogs, or being eaten by jackals, or being eaten by various worms and bugs.

…as a skeleton with flesh and blood, connected by sinews,

…as a skeleton, fleshless, smeared with blood, connected by sinews.

…as a skeleton, flesh and blood all gone, connected by sinews,

Again, bhikshus, you might see this very same woman as random disconnected bones, scattered in all directions, a hand-bone here, a foot-bone there, a shin-bone here, a rib there, a thigh-bone here, a pelvic bone there, a back-bone here, a shoulder-bone there, neck-bone here, a jaw-bone there, a tooth here, a skull there.

What do you think, bhikshus? Have her previous beauty and complexion vanished, the disadvantage (now) evident?”

“Yes, venerable sir.”

“This, bhikshus, is the disadvantage with regards to form.

Again, bhikshus, you might see this very same woman as a corpse, cast aside in a charnel ground, the bones bleached, looking like conch-shells, …the bones piled up over a year old,

…the bones reduced to a powder;

What do you think, bhikshus? Have her previous beauty and complexion vanished, the disadvantage (now) evident?” “Yes, venerable sir.” “This, bhikshus, is the disadvantage with regards to form.

And what, bhikshus, is the escape with regard to form? It is the removal of lustful desire, the giving up of lustful desire for form. This is the escape with regards to form.

It is truly impossible for those ascetics and brahmins who do not understand according to reality gratification as gratification, disadvantage as disadvantage, escape as escape with regards to sense-desires either to fully understand sense-desires through their own practice or to instruct another so that one can fully understand sense-desires.

It is indeed possible for those ascetics and brahmins who do understand them according to reality… either to fully understand sense-desires through their own practice or to instruct another so that one fully understands sense-desires.

Maha Dukkha-k,khandha Sutta

Since you are philosophical, ponder: "What is beauty? Why does it exist? What is its purpose?"

In Buddhism, five questions are always asked about a thing:

(1) How does the thing arise (samudaya)?

(2) How does the thing pass (atthaṅgama)?

(3) What is the attraction (assāda) of the thing?

(4) What is the drawback or danger (ādīnava) of the thing?

(5) What is the method to escape (nissaraṇa) the danger? (which may include, with some things, escaping the danger while utilizing the attractive quality.)

Bhikkhus, the uninstructed worldling does not understand as it really is the origin and the passing away, the gratification, the danger and the escape in the case of form, feeling, perception, volitional formations and consciousness.

But, bhikkhus, the instructed noble disciple understands as it really is the origin and the passing away, the gratification, the danger and the escape in the case of form, feeling, perception, volitional formations and consciousness.

SN 22.74