add scanner_constraints!

src/all_building_blocks/building_blocks.jl

 module BuildingBlocks
 import LinearAlgebra: norm
 import ..BaseBuildingBlocks: BaseBuildingBlock, events, waveform_sequence
-import ...Variables: VariableType, duration, make_generic, get_pulse, get_readout
+import ...Variables: VariableType, duration, make_generic, get_pulse, get_readout, scanner_constraints!
 import ...Components: BaseComponent, DelayedEvent, RFPulseComponent, ReadoutComponent
 
 """

src/variables.jl

@@ -13,8 +13,8 @@ In addition this defines:
 """
 module Variables
 import JuMP: @constraint, @variable, Model, @objective, objective_function, value, AbstractJuMPScalar
-import ..Scanners: gradient_strength, slew_rate
-import ..BuildSequences: global_model
+import ..Scanners: gradient_strength, slew_rate, Scanner
+import ..BuildSequences: global_model, global_scanner
 
 """
 Parent type of all components, building block, and sequences that form an MRI sequence.
@@ -323,4 +323,36 @@ Returns a generic version of the `BaseSequence`, `BaseBuildingBlock`, or `BaseCo
 """
 function make_generic end
 
+
+"""
+    scanner_constraints!(block)
+
+Constraints [`gradient_strength`](@ref) and [`slew_rate`](@ref) to be less than the [`global_scanner`](@ref) maximum.
+"""
+function scanner_constraints!(bb::AbstractBlock)
+    try
+        global_scanner()
+    catch e
+        return
+    end
+    for f in (gradient_strength, slew_rate)
+        try
+            value = gradient_strength(bb)
+        catch e
+            if e isa VariableNotAvailable
+                continue
+            else
+                rethrow()
+            end
+        end
+        if value isa AbstractVector
+            for v in value
+                @constraint global_model() v <= f(global_scanner())
+            end
+        else
+            @constraint global_model() value <= f(global_scanner())
+        end
+    end
+end
+
 end
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