Add RF pulses with slice select

src/gradients/slice_selects.jl

+module SliceSelects
+import JuMP: Model
+import ...BuildingBlocks: RFPulseBlock, ContainerBlock, get_children_blocks
+import ...Variables: VariableType, slice_thickness, get_free_variable, effective_time, start_time, qvec, bmat, qval, bval
+import ...Variables: flip_angle, amplitude, phase, frequency, bandwidth, inverse_bandwidth, N_left, N_right
+import ..ConstantGradientBlocks: ConstantGradientBlock
+
+struct AbstractSliceSelect{T<:VariableType}
+    model :: Model
+    time_before :: T
+    flat_before :: ConstantGradientBlock
+    pulse :: RFPulseBlock
+    time_after :: T
+    flat_after :: ConstantGradientBlock
+    flat_total :: ConstantGradientBlock
+end
+
+"""
+The fixed equivalent of [`SliceSelect`](@ref).
+"""
+const FixedSliceSelect = AbstractSliceSelect{Float64}
+
+"""
+    SliceSelect(gradient_strength, time_before_pulse, pulse, time_after_pulse, rotate, scale)
+
+Represents a slice-selective RF pulse.
+
+This will typically be embedded within a larger gradient waveform.
+Do not create it directly.
+
+The fixed equivalent is [`FixedSliceSelect`](@ref).
+"""
+const SliceSelect = AbstractSliceSelect{VariableType}
+
+function AbstractSliceSelect{VariableType}(model::Model, gradient_strength::SVector{3, VariableType}, time_before_pulse, pulse::RFPulseBlock, time_after_pulse, rotate::Symbol, scale::Symbol)
+    time_before_pulse = get_free_variable(model, time_before_pulse),
+    time_after_pulse = get_free_variable(model, time_after_pulse),
+    return SliceSelect(
+        model,
+        time_before_pulse,
+        ConstantGradientBlock(gradient_strength, time_before_pulse + effective_time(pulse), rotate, scale),
+        pulse,
+        time_after_pulse,
+        ConstantGradientBlock(gradient_strength, duration(pulse) - effective_time(pulse) + time_after_pulse, rotate, scale),
+        ConstantGradientBlock(gradient_strength, duration(pulse) + time_before_pulse + time_after_pulse, rotate, scale),
+    )
+end
+
+
+get_children_blocks(select::SliceSelect) = [(symb, getproperty(select, symb)) for symb in (:flat_before, :pulse, :flat_after)]
+Base.get_index(select::SliceSelect, index::Symbol) = getproperty(select, index)
+
+start_time(select::SliceSelect, symbol::Symbol) = start_time(select, Val(symbol))
+start_time(select::SliceSelect, ::Val{:flat_before}) = 0.
+start_time(select::SliceSelect, ::Val{:pulse}) = select.time_before_pulse
+start_time(select::SliceSelect, ::Val{:flat_after}) = duration(select.flat_before)
+start_time(select::SliceSelect, ::Val{:flat_total}) = 0.
+
+qvec(select::SliceSelect) = qvec(select.flat_total)
+bmat(select::SliceSelect) = bmat(select.flat_total)
+duration(select::SliceSelect) = duration(select.flat_total)
+gradient_strength(select::SliceSelect) = gradient_strength(select.flat_total)
+slice_thickness(select::SliceSelect) = bandwidth(select) ./ gradient_strength(select)
+
+for fn in (flip_angle, amplitude, phase, frequency, bandwidth, inverse_bandwidth, N_left, N_right)
+    @eval $fn(select::SliceSelect) = $fn(select.pulse)
+end
+
+variables(::Type{<:SliceSelect}) = (duration, gradient_strength, slice_thickness, qvec, bmat, qval, bval, flip_angle, amplitude, phase, frequency, bandwidth, inverse_bandwidth, N_left, N_right)
+
+end
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