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Equation 13 · Part 15 · How Multimodal Models Actually Handle Video, Audio, and Space

Ending index or upper bound: t

C(r)=∫tntfT(t) σ(r(t)) c(r(t),d) dt,T(t)=exp⁡ ⁣(−∫tntσ(r(s)) ds),C(\mathbf{r}) = \int_{t_n}^{t_f} T(t)\, \sigma(\mathbf{r}(t))\, \mathbf{c}(\mathbf{r}(t), \mathbf{d})\, dt, \qquad T(t) = \exp\!\left(-\int_{t_n}^{t} \sigma(\mathbf{r}(s))\, ds\right),
tt

What this part means

This label says where the repeated addition, multiplication, or accumulation stops. It sets the last term or end of the range.

Its job in the formula

t appears in the bound of this integral. The bound states where the repeated operation starts, ends, or which values it includes.

The passage around this formula

…see by integrating along it [ 8 ] . The rendering equation itself is the cleanest statement of what “continuous” buys and costs: C(r)=∫tntfT(t) σ(r(t)) c(r(t),d) dt,T(t)=exp⁡ ⁣(−∫tntσ(r(s)) ds)C(\mathbf{r}) = \int_{t_n}^{t_f} T(t)\, \sigma(\mathbf{r}(t))\, \mathbf{c}(\mathbf{r}(t), \mathbf{d})\, dt, \qquad T(t) = \exp\!\left(-\int_{t_n}^{t} \sigma(\mathbf{r}(s))\, ds\right). where σ\sigma is volume density, c\mathbf{c} is emitted colour, and T(t) is accumulated transmittance along the ray up to t . There is no patch, no voxel grid, no fixed token count anywhere in this formulation — the scene is a function evaluated at query points, and any tokenization of it for a downstream language model has to be imposed afterward, by sampling the…

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Learn the underlying idea

Σ adds a collection of terms. Π multiplies them. The lower and upper labels tell you which terms belong to the collection.

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Sources cited in the surrounding passage

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