saliency.hpp

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#pragma once
 
#include <stdexcept>
#include <string>
#include <vector>
 
#include "pulsatrix/assert.hpp"
#include "pulsatrix/attribution.hpp"
#include "pulsatrix/device_backend.hpp"
#include "pulsatrix/explainer_context.hpp"
#include "pulsatrix/tensor.hpp"
 
namespace pulsatrix {
 
class Saliency {
public:
    [[nodiscard]] Attribution explain(ExplainerContext& ctx, const Tensor& input, int64_t target_index,
                                       DeviceBackend* backend) const {
        Tensor output = ctx.forward_pass(input);
        // External boundary (Mission 2, finding 15 systemic sweep; rank check added by
        // campaign_exai_dl_library_batch_dimension_support) -- escalated from
        // PULSATRIX_ASSERT-only.
        if (output.rank() != 2) {
            throw std::invalid_argument("Saliency::explain: network output must be rank-2 (N, num_classes)");
        }
        if (target_index < 0 || target_index >= output.shape().dim(1)) {
            throw std::invalid_argument("Saliency::explain: target_index out of range");
        }
        int64_t N = output.shape().dim(0);
        int64_t C = output.shape().dim(1);
 
        std::vector<float> seed_values(static_cast<size_t>(output.numel()), 0.0f);
        for (int64_t n = 0; n < N; ++n) {
            seed_values[static_cast<size_t>(n * C + target_index)] = 1.0f;
        }
        Tensor seed(output.shape(), explainer_detail::backend_beside(output, backend), seed_values,
                    output.device());
 
        Tensor grad = ctx.backward_pass(seed);
 
        // Attribution has no default constructor -- Tensor (its values member) doesn't
        // either, by design (Phase 0). Aggregate-initialize directly instead.
        return Attribution{"saliency", std::move(grad), {{"target_index", std::to_string(target_index)}}};
    }
};
 
}  // namespace pulsatrix